Merge branch 'dm-queue-mirror-jobs-in-batches-drain-ce' into 'master'

Add queue_size method to ApplicationWorker

See merge request gitlab-org/gitlab-ce!30416

app/workers/concerns/application_worker.rb

 # frozen_string_literal: true
+require 'sidekiq/api'
+
 Sidekiq::Worker.extend ActiveSupport::Concern
 module ApplicationWorker
@@ -44,6 +46,10 @@ module ApplicationWorker
       get_sidekiq_options['queue'].to_s
     end
+    def queue_size
+      Sidekiq::Queue.new(queue).size
+    end
+
     def bulk_perform_async(args_list)
       Sidekiq::Client.push_bulk('class' => self, 'args' => args_list)
     end