DEV: move post flags into database (#27125)

This is preparation for a feature that will allow admins to define their custom flags. Current behaviour should stay untouched.

spec/fabricators/flag_fabricator.rb

@@ -1,7 +1,3 @@
 # frozen_string_literal: true
 
-Fabricator(:flag, from: :post_action) do
-  user
-  post
-  post_action_type_id PostActionType.types[:spam]
-end
+Fabricator(:flag) { name "offtopic", applies_to { %w[Post Chat::Message] } }