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.

lib/mastodon/migration_warning.rb

@@ -0,0 +1,55 @@
+# frozen_string_literal: true
+
+module Mastodon
+  module MigrationWarning
+    WARNING_SECONDS = 10
+
+    DEFAULT_WARNING = <<~WARNING_MESSAGE
+      WARNING: This migration may take a *long* time for large instances.
+      It will *not* lock tables for any significant time, but it may run
+      for a very long time. We will pause for #{WARNING_SECONDS} seconds to allow you to
+      interrupt this migration if you are not ready.
+    WARNING_MESSAGE
+
+    def migration_duration_warning(explanation = nil)
+      return unless valid_environment?
+
+      announce_warning(explanation)
+
+      announce_countdown
+    end
+
+    private
+
+    def announce_countdown
+      WARNING_SECONDS.downto(1) do |i|
+        say "Continuing in #{i} second#{i == 1 ? '' : 's'}...", true
+        sleep 1
+      end
+    end
+
+    def valid_environment?
+      $stdout.isatty && Rails.env.production?
+    end
+
+    def announce_warning(explanation)
+      announce_message prepare_message(explanation)
+    end
+
+    def announce_message(text)
+      say ''
+      text.each_line do |line|
+        say(line)
+      end
+      say ''
+    end
+
+    def prepare_message(explanation)
+      if explanation.blank?
+        DEFAULT_WARNING
+      else
+        DEFAULT_WARNING + "\n#{explanation}"
+      end
+    end
+  end
+end