Worker monitoring feature: needed improvements

[Didayolo]

The worker monitoring feature got merged:

• Worker status/monitoring for competition organizers (from rabbit) #2395

Remaining TODO:

• Add documentation
• In "monitor queues" interface:
  • Add an option to filter queues with no workers
  • Option to see the competitions linked to a queue
  • Queue "default" should be clearly identified and at the top of the table
• Check if there is a problem with the number of "Pending" and "Running" jobs