v0.23.0

This release was intended to be mainly a code reorganisation and refactoring, significantly improving the maintainability of the codebase. This should allow us to improve further and make it easier for the maintainers to keep on top of the project.
However, as you all have noticed, it turned out to become a much larger, much longer release cycle than anticipated. It has ended up to be a release with a lot of rewrites and changes to the code base and functionality of Headscale, cleaning up a lot of technical debt and introducing a lot of improvements. This does come with some breaking changes,

**Please remember to always back up your database between versions**

#### Here is a short summary of the broad topics of changes:

Code has been organised into modules, reducing use of global variables/objects, isolating concerns and “putting the right things in the logical place”.

The new [policy](https://github.com/juanfont/headscale/tree/main/hscontrol/policy) and [mapper](https://github.com/juanfont/headscale/tree/main/hscontrol/mapper) package, containing the ACL/Policy logic and the logic for creating the data served to clients (the network “map”) has been rewritten and improved. This change has allowed us to finish SSH support and add additional tests throughout the code to ensure correctness.

The [“poller”, or streaming logic](https://github.com/juanfont/headscale/blob/main/hscontrol/poll.go) has been rewritten and instead of keeping track of the latest updates, checking at a fixed interval, it now uses go channels, implemented in our new [notifier](https://github.com/juanfont/headscale/tree/main/hscontrol/notifier) package and it allows us to send updates to connected clients immediately. This should both improve performance and potential latency before a client picks up an update.

Headscale now supports sending “delta” updates, thanks to the new mapper and poller logic, allowing us to only inform nodes about new nodes, changed nodes and removed nodes. Previously we sent the entire state of the network every time an update was due.

While we have a pretty good [test harness](https://github.com/search?q=repo%3Ajuanfont%2Fheadscale+path%3A_test.go&type=code) for validating our changes, the changes came down to [284 changed files with 32,316 additions and 24,245 deletions](https://github.com/juanfont/headscale/compare/b01f1f1867136d9b2d7b1392776eb363b482c525...ed78ecd) and bugs are expected. We need help testing this release. In addition, while we think the performance should in general be better, there might be regressions in parts of the platform, particularly where we prioritised correctness over speed.

There are also several bugfixes that has been encountered and fixed as part of implementing these changes, particularly
after improving the test harness as part of adopting [#1460](https://github.com/juanfont/headscale/pull/1460).

### BREAKING

- Code reorganisation, a lot of code has moved, please review the following PRs accordingly [#1473](https://github.com/juanfont/headscale/pull/1473)
- Change the structure of database configuration, see [config-example.yaml](./config-example.yaml) for the new structure. [#1700](https://github.com/juanfont/headscale/pull/1700)
  - Old structure has been remove and the configuration _must_ be converted.
  - Adds additional configuration for PostgreSQL for setting max open, idle connection and idle connection lifetime.
- API: Machine is now Node [#1553](https://github.com/juanfont/headscale/pull/1553)
- Remove support for older Tailscale clients [#1611](https://github.com/juanfont/headscale/pull/1611)
  - The oldest supported client is 1.42
- Headscale checks that _at least_ one DERP is defined at start [#1564](https://github.com/juanfont/headscale/pull/1564)
  - If no DERP is configured, the server will fail to start, this can be because it cannot load the DERPMap from file or url.
- Embedded DERP server requires a private key [#1611](https://github.com/juanfont/headscale/pull/1611)
  - Add a filepath entry to [`derp.server.private_key_path`](https://github.com/juanfont/headscale/blob/b35993981297e18393706b2c963d6db882bba6aa/config-example.yaml#L95)
- Docker images are now built with goreleaser (ko) [#1716](https://github.com/juanfont/headscale/pull/1716) [#1763](https://github.com/juanfont/headscale/pull/1763)
  - Entrypoint of container image has changed from shell to headscale, require change from `headscale serve` to `serve`
  - `/var/lib/headscale` and `/var/run/headscale` is no longer created automatically, see [container docs](./docs/running-headscale-container.md)
- Prefixes are now defined per v4 and v6 range. [#1756](https://github.com/juanfont/headscale/pull/1756)
  - `ip_prefixes` option is now `prefixes.v4` and `prefixes.v6`
  - `prefixes.allocation` can be set to assign IPs at `sequential` or `random`. [#1869](https://github.com/juanfont/headscale/pull/1869)
- MagicDNS domains no longer contain usernames []()
  - This is in preperation to fix Headscales implementation of tags which currently does not correctly remove the link between a tagged device and a user. As tagged devices will not have a user, this will require a change to the DNS generation, removing the username, see [#1369](https://github.com/juanfont/headscale/issues/1369) for more information.
  - `use_username_in_magic_dns` can be used to turn this behaviour on again, but note that this option _will be removed_ when tags are fixed.
    - dns.base_domain can no longer be the same as (or part of) server_url.
    - This option brings Headscales behaviour in line with Tailscale.
- YAML files are no longer supported for headscale policy. [#1792](https://github.com/juanfont/headscale/pull/1792)
  - HuJSON is now the only supported format for policy.
- DNS configuration has been restructured [#2034](https://github.com/juanfont/headscale/pull/2034)
  - Please review the new [config-example.yaml](./config-example.yaml) for the new structure.

### Changes

- Use versioned migrations [#1644](https://github.com/juanfont/headscale/pull/1644)
- Make the OIDC callback page better [#1484](https://github.com/juanfont/headscale/pull/1484)
- SSH support [#1487](https://github.com/juanfont/headscale/pull/1487)
- State management has been improved [#1492](https://github.com/juanfont/headscale/pull/1492)
- Use error group handling to ensure tests actually pass [#1535](https://github.com/juanfont/headscale/pull/1535) based on [#1460](https://github.com/juanfont/headscale/pull/1460)
- Fix hang on SIGTERM [#1492](https://github.com/juanfont/headscale/pull/1492) taken from [#1480](https://github.com/juanfont/headscale/pull/1480)
- Send logs to stderr by default [#1524](https://github.com/juanfont/headscale/pull/1524)
- Fix [TS-2023-006](https://tailscale.com/security-bulletins/#ts-2023-006) security UPnP issue [#1563](https://github.com/juanfont/headscale/pull/1563)
- Turn off gRPC logging [#1640](https://github.com/juanfont/headscale/pull/1640) fixes [#1259](https://github.com/juanfont/headscale/issues/1259)
- Added the possibility to manually create a DERP-map entry which can be customized, instead of automatically creating it. [#1565](https://github.com/juanfont/headscale/pull/1565)
- Add support for deleting api keys [#1702](https://github.com/juanfont/headscale/pull/1702)
- Add command to backfill IP addresses for nodes missing IPs from configured prefixes. [#1869](https://github.com/juanfont/headscale/pull/1869)
- Log available update as warning [#1877](https://github.com/juanfont/headscale/pull/1877)
- Add `autogroup:internet` to Policy [#1917](https://github.com/juanfont/headscale/pull/1917)
- Restore foreign keys and add constraints [#1562](https://github.com/juanfont/headscale/pull/1562)
- Make registration page easier to use on mobile devices
- Make write-ahead-log default on and configurable for SQLite [#1985](https://github.com/juanfont/headscale/pull/1985)
- Add APIs for managing headscale policy. [#1792](https://github.com/juanfont/headscale/pull/1792)
- Fix for registering nodes using preauthkeys when running on a postgres database in a non-UTC timezone. [#764](https://github.com/juanfont/headscale/issues/764)
- Make sure integration tests cover postgres for all scenarios
- CLI commands (all except `serve`) only requires minimal configuration, no more errors or warnings from unset settings [#2109](https://github.com/juanfont/headscale/pull/2109)
- CLI results are now concistently sent to stdout and errors to stderr [#2109](https://github.com/juanfont/headscale/pull/2109)
- Fix issue where shutting down headscale would hang [#2113](https://github.com/juanfont/headscale/pull/2113)

### Changelog
* e9d9c0773c6acd8db3e4a0759e0d2cd98163e696 Exclude irrelevant files from mkdocs rendering (#2136)
* ed78ecda12d86ffe115e4a10172376f887ac82a1 add shutdown that asserts if headscale had panics (#2126)
* 6cbbcd859c815031730f035fd8f3ca90d05cf522 flake.lock: Update (#2135)
* 10a72e8d542af68c0c280f2a6ccc84849719b24c update changelog for 0.23 release (#2138)