Make EmailsOnPushWorker use Sidekiq mailers queue
A customer was having issues with EmailsOnPushWorker clogging the Sidekiq queues and merge requests not being handled quickly. While researching whether it would possible to spin up a separate Sidekiq task just to handle merge requests and other key functions, I found that this worker was using the default Sidekiq queue. Moving to the mailers
queue makes it possible to de-prioritize this worker and give more weight to the others.