Add option for cron processing of queue

I agree a UI option to enable/disable cron processing of the queue would be ideal. But as a workaround, here's some code I've added to a custom module to make the cron process the queue:

/**
 * Implement hook_cron()
 */
function MYMODULE_cron()
{
  $queue_worker = \Drupal::service('plugin.manager.queue_worker');
  $bulletinQueue_worker = $queue_worker->createInstance('govdelivery_bulletins');
  $bulletinQueue_worker->processQueue();
}

(Replace MYMODULE with the name of your custom module.)