Merge branch 'main' into glitch-soc/merge-upstream

Merge branch 'main' into glitch-soc/merge-upstream

Conflicts:
- `app/serializers/rest/instance_serializer.rb`:
  Upstream changed the fields returned by /api/v1/instance by adding a
  `configuration` field holding a lot of useful information making our
  `max_toot_chars` and `poll_limits` fields obsolete.
  Keeping those around for now for compatibility.
- `app/validators/status_length_validator.rb`:
  No real conflict, just URL_PLACEHOLDER_CHARS introduced too close to
  MAX_CHARS which is defined differently in glitch-soc.
  Ported upstream changes.