DEV: Convert min_trust_to_create_topic to groups (#24740)

This change converts the min_trust_to_create_topic site setting to
create_topic_allowed_groups.

See: https://meta.discourse.org/t/283408

- Hides the old setting
- Adds the new site setting
- Add a deprecation warning
- Updates to use the new setting
- Adds a migration to fill in the new setting if the old setting was
changed
- Adds an entry to the site_setting.keywords section
- Updates tests to account for the new change
- After a couple of months, we will remove the min_trust_to_create_topicsetting entirely.

Internal ref: /t/117248

spec/models/user_spec.rb

@@ -1339,7 +1339,7 @@ RSpec.describe User do
   end
 
   describe "flag_linked_posts_as_spam" do
-    fab!(:user)
+    fab!(:user) { Fabricate(:user, refresh_auto_groups: true) }
     fab!(:admin)
     fab!(:post) do
       PostCreator.new(