feat(perf): Cache labels on the conversation model (#8527)

app/models/conversation.rb

@@ -6,6 +6,7 @@
 #  additional_attributes  :jsonb
 #  agent_last_seen_at     :datetime
 #  assignee_last_seen_at  :datetime
+#  cached_label_list      :string
 #  contact_last_seen_at   :datetime
 #  custom_attributes      :jsonb
 #  first_reply_created_at :datetime
@@ -144,10 +145,6 @@ class Conversation < ApplicationRecord
     end
   end
 
-  def update_assignee(agent = nil)
-    update!(assignee: agent)
-  end
-
   def toggle_status
     # FIXME: implement state machine with aasm
     self.status = open? ? :resolved : :open
@@ -185,6 +182,10 @@ class Conversation < ApplicationRecord
     Conversations::EventDataPresenter.new(self).push_data
   end
 
+  def cached_label_list_array
+    (cached_label_list || '').split(',')
+  end
+
   def notifiable_assignee_change?
     return false unless saved_change_to_assignee_id?
     return false if assignee_id.blank?