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

Conflicts:
- `README.md`:
  Upstream added a link to the roadmap, but we have a completely different README.
  Kept ours.
- `app/models/media_attachment.rb`:
  Upstream upped media attachment limits.
  Updated the default according to upstream's.
- `db/migrate/20180831171112_create_bookmarks.rb`:
  Upstream changed the migration compatibility level.
  Did so too.
- `config/initializers/content_security_policy.rb`:
  Upstream refactored this file but we have a different version.
  Kept our version.
- `app/controllers/settings/preferences_controller.rb`:
  Upstream completely refactored user settings storage, and glitch-soc has a
  different set of settings.
  The file does not directly references individual settings anymore.
  Applied upstream changes.
- `app/lib/user_settings_decorator.rb`:
  Upstream completely refactored user settings storage, and glitch-soc has a
  different set of settings.
  The file got removed entirely.
  Removed it as well.
- `app/models/user.rb`:
  Upstream completely refactored user settings storage, and glitch-soc has a
  different set of settings.
  References to individual settings have been removed from the file.
  Removed them as well.
- `app/views/settings/preferences/appearance/show.html.haml`:
  Upstream completely refactored user settings storage, and glitch-soc has a
  different set of settings.
  Applied upstream's changes and ported ours back.
- `app/views/settings/preferences/notifications/show.html.haml`:
  Upstream completely refactored user settings storage, and glitch-soc has a
  different set of settings.
  Applied upstream's changes and ported ours back.
- `app/views/settings/preferences/other/show.html.haml`:
  Upstream completely refactored user settings storage, and glitch-soc has a
  different set of settings.
  Applied upstream's changes and ported ours back.
- `config/settings.yml`:
  Upstream completely refactored user settings storage, and glitch-soc has a
  different set of settings.
  In particular, upstream removed user-specific and unused settings.
  Did the same in glitch-soc.
- `spec/controllers/application_controller_spec.rb`:
  Conflicts due to glitch-soc's theming system.
  Mostly kept our version, as upstream messed up the tests.

app/controllers/concerns/account_controller_concern.rb

@@ -10,7 +10,8 @@ module AccountControllerConcern
 
   included do
     before_action :set_instance_presenter
-    before_action :set_link_headers, if: -> { request.format.nil? || request.format == :html }
+
+    after_action :set_link_headers, if: -> { request.format.nil? || request.format == :html }
   end
 
   private