DEV: Convert min_trust_to_post_links to groups (#25298)

We're changing the implementation of trust levels to use groups. Part of this is to have site settings that reference trust levels use groups instead. It converts the min_trust_to_post_links  site setting to post_links_allowed_groups.

This isn't used by any of our plugins or themes, so very little fallout.

spec/lib/post_revisor_spec.rb

@@ -854,7 +854,7 @@ RSpec.describe PostRevisor do
     end
 
     describe "admin editing a new user's post" do
-      fab!(:changed_by) { Fabricate(:admin) }
+      fab!(:changed_by) { Fabricate(:admin, refresh_auto_groups: true) }
 
       before do
         SiteSetting.newuser_max_embedded_media = 0