v2.4.3

Guess what: this is our 100th release! :tada: :partying_face: :confetti_ball: 

A bug fix for the bug fix, and a couple other bug fixes, including one security fix for PHP sites. We think all users should upgrade after giving it a whirl in their test environments. Please note some changes in this patch:

- :warning: **In `reverse_proxy`, the `max_idle_conns_per_host` option has been removed (both Caddyfile and JSON).** This may be a breaking change for a few of you, but it only breaks configs that relied on a bug. Instead of silently failing, you will get an error if you continue using the property. For Caddyfile, we basically renamed the property to `keepalive_idle_conns_per_host`. In JSON, we simply removed the property, and you should instead set `keep_alive/max_idle_conns_per_host` if you weren't already. Previously, the Caddyfile subdirective set both MaxConnsPerHost and MaxIdleConnsPerHost, which was confusing; and the JSON properties overwrote each other, so one was removed. Issue #4201.
- **:shield: Security patch** in the FastCGI transport that now sanitizes paths against directory traversal outside the site root. PR #4207.
- **:bug: Fix canonicalization redirects in `file_server`.** v2.4.2 introduced a bugfix (#4179) for these redirects when used inside `handle_path` (i.e. rewriting the path by stripping a prefix), but caused a regression for many other use cases. This release includes a proper fix for all known, tested cases. Basically: these redirects are not issued if the filename of a path was rewritten internally. Issue #4205.

## Changelog

9d4ed3a3 caddyhttp: Refactor and export SanitizedPathJoin for use in fastcgi (#4207)
e8ae80ad fileserver: Don't persist parsed template (fix #4202)
fbd65609 fileserver: Only redirect if filename not rewritten (fix #4205)
32c284b5 reverseproxy: Adjust test related to #4201
7c68809f reverseproxy: Fix overwriting of max_idle_conns_per_host (closes #4201)