Add configuration option to filter replies in lists (#9205)

* Add database support for list show-reply preferences

* Add backend support to read and update list-specific show_replies settings

* Add basic UI to set list replies setting

* Add specs for list replies policy

* Switch "cycling" reply policy link to a set of radio inputs

* Capitalize replies_policy strings

* Change radio button design to be consistent with that of the directory explorer

app/serializers/rest/list_serializer.rb

@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
 class REST::ListSerializer < ActiveModel::Serializer
-  attributes :id, :title
+  attributes :id, :title, :replies_policy
 
   def id
     object.id.to_s