feat: use gin index for message search (#11107)

This PR updates the search implementation to better utilize the GIN
indexes. The option is toggled behind a feature flag for us to test it
internally before making it available publicly

config/features.yml

@@ -154,3 +154,6 @@
   display_name: Contact Chatwoot Support Team
   enabled: true
   chatwoot_internal: true
+- name: search_with_gin
+  display_name: Search messages with GIN
+  enabled: false