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

app/jobs/migration/conversation_cache_label_job.rb

@@ -0,0 +1,16 @@
+class Migration::ConversationCacheLabelJob < ApplicationJob
+  queue_as :async_database_migration
+
+  # To cache the label, we simply access it from the object and save it. Anytime the object is
+  # saved in the future, ActsAsTaggable will automatically recompute it. This process is done
+  # initially when the user has not performed any action.
+  # Reference: https://github.com/mbleigh/acts-as-taggable-on/wiki/Caching
+  def perform(account)
+    account.conversations.find_in_batches do |conversation_batch|
+      conversation_batch.each do |conversation|
+        conversation.label_list
+        conversation.save!
+      end
+    end
+  end
+end