Merge tag 'v1.56.0rc1' into develop

Synapse 1.56.0rc1 (2022-03-29)
==============================

Features
--------

- Allow modules to store already existing 3PID associations. ([\#12195](#12195))
- Allow registering server administrators using the module API. Contributed by Famedly. ([\#12250](#12250))

Bugfixes
--------

- Fix a long-standing bug which caused the `/_matrix/federation/v1/state` and `/_matrix/federation/v1/state_ids` endpoints to return incorrect or invalid data when called for an event which we have stored as an "outlier". ([\#12087](#12087))
- Fix a long-standing bug where events from ignored users would still be considered for relations. ([\#12227](#12227), [\#12232](#12232), [\#12285](#12285))
- Fix a bug introduced in Synapse 1.53.0 where an unnecessary query could be performed when fetching bundled aggregations for threads. ([\#12228](#12228))
- Fix a bug introduced in Synapse 1.52.0 where admins could not deactivate and GDPR-erase a user if Synapse was configured with limits on avatars. ([\#12261](#12261))

Improved Documentation
----------------------

- Fix the link to the module documentation in the legacy spam checker warning message. ([\#12231](#12231))
- Remove incorrect prefixes in the worker documentation for some endpoints. ([\#12243](#12243))
- Correct `check_username_for_spam` annotations and docs. ([\#12246](#12246))
- Correct Authentik OpenID typo, and add notes on troubleshooting. Contributed by @IronTooch. ([\#12275](#12275))
- HAProxy reverse proxy guide update to stop sending IPv4-mapped address to homeserver. Contributed by @villepeh. ([\#12279](#12279))

Internal Changes
----------------

- Rename `shared_rooms` to `mutual_rooms` ([MSC2666](matrix-org/matrix-spec-proposals#2666)), as per proposal changes. ([\#12036](#12036))
- Remove check on `update_user_directory` for shared rooms handler ([MSC2666](matrix-org/matrix-spec-proposals#2666)), and update/expand documentation. ([\#12038](#12038))
- Refactor `create_new_client_event` to use a new parameter, `state_event_ids`, which accurately describes the usage with [MSC2716](matrix-org/matrix-spec-proposals#2716) instead of abusing `auth_event_ids`. ([\#12083](#12083), [\#12304](#12304))
- Refuse to start if registration is enabled without email, captcha, or token-based verification unless the new config flag `enable_registration_without_verification` is set. ([\#12091](#12091))
- Add tests for database transaction callbacks. ([\#12198](#12198))
- Handle cancellation in `DatabasePool.runInteraction`. ([\#12199](#12199))
- Add missing type hints for cache storage. ([\#12216](#12216))
- Add missing type hints for storage. ([\#12248](#12248), [\#12255](#12255))
- Add type hints to tests files. ([\#12224](#12224), [\#12240](#12240), [\#12256](#12256))
- Use type stubs for `psycopg2`. ([\#12269](#12269))
- Improve type annotations for `execute_values`. ([\#12311](#12311))
- Clean-up logic around rebasing URLs for URL image previews. ([\#12219](#12219))
- Use the `ignored_users` table in additional places instead of re-parsing the account data. ([\#12225](#12225))
- Refactor the relations endpoints to add a `RelationsHandler`. ([\#12237](#12237))
- Generate announcement links in the release script. ([\#12242](#12242))
- Improve error message when dependencies check finds a broken installation. ([\#12244](#12244))
- Compress metrics HTTP resource when enabled. Contributed by Nick @ Beeper. ([\#12258](#12258))
- Refuse to start if the PostgreSQL database has a non-`C` locale, unless the config flag `allow_unsafe_db_locale` is set to true. ([\#12262](#12262), [\#12288](#12288))
- Optionally include account validity expiration information to experimental [MSC3720](matrix-org/matrix-spec-proposals#3720) account status responses. ([\#12266](#12266))
- Add a new cache `_get_membership_from_event_id` to speed up push rule calculations in large rooms. ([\#12272](#12272))
- Re-enable Complement concurrency in CI. ([\#12283](#12283))
- Remove unused test utilities. ([\#12291](#12291))
- Enhance logging for inbound federation events. ([\#12301](#12301))
- Fix compatibility with the recently-released Jinja 3.1. ([\#12313](#12313))
- Avoid trying to calculate the state at outlier events. ([\#12314](#12314))

Author: richvdh