feat(perf): improve performance of conversation filter API [CW-1605] (#7120)

* feat(perf): don't use count

* feat(perf): include messages in the conversation query

* feat: include contact inboxes

* refactor: use blank?

app/services/conversations/filter_service.rb

@@ -58,8 +58,9 @@ class Conversations::FilterService < FilterService
 
   def conversations
     @conversations = @conversations.includes(
-      :taggings, :inbox, { assignee: { avatar_attachment: [:blob] } }, { contact: { avatar_attachment: [:blob] } }, :team
+      :taggings, :inbox, { assignee: { avatar_attachment: [:blob] } }, { contact: { avatar_attachment: [:blob] } }, :team, :messages, :contact_inbox
     )
+
     @conversations.latest.page(current_page)
   end
 end