Merge commit '877090518682b6c77ba9bdfa0231afd56daec44d' into glitch-soc/merge-upstream

Conflicts:
- `app/models/concerns/user/has_settings.rb`:
  Not a real conflict, upstream added a setting textually close to a glitch-soc one.
  Added upstream's new setting.
- `app/views/settings/preferences/appearance/show.html.haml`:
  Not a real conflict, upstream added a setting textually close to a glitch-soc one.
  Added upstream's new setting.
- `config/routes.rb`:
  Upstream moved web app routes to `config/routes/web_app.rb`, while glitch-soc had
  an extra route.
  Moved the extra route to `config/routes/web_app.rb`.
- `spec/controllers/settings/preferences/appearance_controller_spec.rb`:
  This spec got converted to a system spec upstream.
  However, the theme setting works differently in glitch-soc, so the spec had been
  changed.
  Changed the corresponding system spec as well.

spec/requests/api/v2/instance_spec.rb

@@ -55,6 +55,9 @@ RSpec.describe 'Instances' do
             max_characters: StatusLengthValidator::MAX_CHARS,
             max_media_attachments: Status::MEDIA_ATTACHMENTS_LIMIT
           ),
+          media_attachments: include(
+            description_limit: MediaAttachment::MAX_DESCRIPTION_LENGTH
+          ),
           polls: include(
             max_options: PollValidator::MAX_OPTIONS
           )