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.

app/validators/status_length_validator.rb

@@ -2,7 +2,8 @@
 
 class StatusLengthValidator < ActiveModel::Validator
   MAX_CHARS = (ENV['MAX_TOOT_CHARS'] || 500).to_i
-  URL_PLACEHOLDER = "\1#{'x' * 23}"
+  URL_PLACEHOLDER_CHARS = 23
+  URL_PLACEHOLDER = "\1#{'x' * URL_PLACEHOLDER_CHARS}"
 
   def validate(status)
     return unless status.local? && !status.reblog?