backend/v2.2.1

A smaller release, but with some important fixes and improvements. Most notably:
- Flow locking mechanism to prevent concurrent execution of the same flow, addressing possible race conditions and side effects in actions (setting header tokens, sending emails, ...) in concurrent request scenarios
- Option to configure (or omit) the 3rd-party `prompt` parameter to fine-tune the social SSO UX
- Hanko Elements attributes working again (e.g. prefilled email or the mode attribute)
- Hanko Elements UI fixes

## What's Changed
* fix: consistently use persisters with connection by @lfleischmann in https://github.com/teamhanko/hanko/pull/2276
* fix: don't show the divider on login by @FreddyDevelop in https://github.com/teamhanko/hanko/pull/2277
* fix: unwarranted passcode data in webhooks by @lfleischmann in https://github.com/teamhanko/hanko/pull/2279
* feat: add last used badge by @FreddyDevelop in https://github.com/teamhanko/hanko/pull/2283
* fix: ensure WebAuthn session data expires time is in UTC by @FreddyDevelop in https://github.com/teamhanko/hanko/pull/2287
* feat: add flow locking mechanism by @lfleischmann in https://github.com/teamhanko/hanko/pull/2285
* docs: fix redis config password schema by @lfleischmann in https://github.com/teamhanko/hanko/pull/2293
* feat: change default thirdparty prompt parameter behaviour by @lfleischmann in https://github.com/teamhanko/hanko/pull/2292
* fix: elements attribute handling by @lfleischmann in https://github.com/teamhanko/hanko/pull/2295


**Full Changelog**: https://github.com/teamhanko/hanko/compare/backend/v2.2.0...backend/v2.2.1