DEV: Added callback to change the query used to filter groups in search (#19884)

Added plugin registry that will allow adding callbacks that can change the query that is used
to filter groups while running a search.

lib/discourse_plugin_registry.rb

@@ -106,6 +106,8 @@ class DiscoursePluginRegistry
   define_filtered_register :hashtag_autocomplete_data_sources
   define_filtered_register :hashtag_autocomplete_contextual_type_priorities
 
+  define_filtered_register :search_groups_set_query_callbacks
+
   def self.register_auth_provider(auth_provider)
     self.auth_providers << auth_provider
   end