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.

Gemfile.lock

@@ -492,7 +492,6 @@ GEM
     regexp_parser (2.1.1)
     request_store (1.5.0)
       rack (>= 1.4)
-    resolv (0.1.0)
     responders (3.0.1)
       actionpack (>= 5.0)
       railties (>= 5.0)
@@ -525,7 +524,7 @@ GEM
     rspec-support (3.10.2)
     rspec_junit_formatter (0.4.1)
       rspec-core (>= 2, < 4, != 2.12.0)
-    rubocop (1.18.2)
+    rubocop (1.18.3)
       parallel (~> 1.10)
       parser (>= 3.0.0.0)
       rainbow (>= 2.2.2, < 4.0)
@@ -766,7 +765,6 @@ DEPENDENCIES
   redcarpet (~> 3.5)
   redis (~> 4.3)
   redis-namespace (~> 1.8)
-  resolv (~> 0.1.0)
   rqrcode (~> 2.0)
   rspec-rails (~> 5.0)
   rspec-sidekiq (~> 3.1)