Initialize Sidekiq with the list of queues used by GitLab

The Sidekiq client API adds an entry to the Sidekiq "queues" list,
but mail_room and gitlab-shell use redis-rb directly to insert jobs
into Redis and thus do not make an extra "sadd" call to Redis
each time a job is inserted. To make it possible to monitor
these queues via the API, add an initialization step to
set up the list at startup.

Closes gitlab-com/infrastructure#682

CHANGELOG.md

@@ -39,6 +39,7 @@ Please view this file on the master branch, on stable branches it's out of date.
 - Fix Sign in page 'Forgot your password?' link overlaps on medium-large screens
 - Show full status link on MR & commit pipelines
 - Fix documents and comments on Build API `scope`
+- Initialize Sidekiq with the list of queues used by GitLab
 - Refactor email, use setter method instead AR callbacks for email attribute (Semyon Pupkov)
 - Shortened merge request modal to let clipboard button not overlap
 - In all filterable drop downs, put input field in focus only after load is complete (Ido @leibo)

config/initializers/sidekiq.rb

@@ -42,3 +42,19 @@ end
 Sidekiq.configure_client do |config|
   config.redis = redis_config_hash
 end
+
+# The Sidekiq client API always adds the queue to the Sidekiq queue
+# list, but mail_room and gitlab-shell do not. This is only necessary
+# for monitoring.
+config = YAML.load_file(Rails.root.join('config', 'sidekiq_queues.yml').to_s)
+
+begin
+  Sidekiq.redis do |conn|
+    conn.pipelined do
+      config[:queues].each do |queue|
+        conn.sadd('queues', queue[0])
+      end
+    end
+  end
+rescue Redis::BaseError, SocketError
+end