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/cooked_post_processor_spec.rb

@@ -184,9 +184,11 @@ RSpec.describe CookedPostProcessor do
              - #{url_with_query_param}
           RAW
 
-        let(:staff_post) { Fabricate(:post, user: Fabricate(:admin), raw: <<~RAW) }
+        let(:staff_post) do
+          Fabricate(:post, user: Fabricate(:admin, refresh_auto_groups: true), raw: <<~RAW)
           This is a #{url_with_path} topic
           RAW
+        end
 
         before do
           urls.each do |url|