Keep track of running agents

Current situation

The GET /agents endpoint does not tell if an agent is busy or not.

Desired outcome

The GET /agents endpoint returns this information, in the form of the job ID it is currently processing.

# ...
    status:
      communicationCount: 0
      communicationStatusSummary: {}
      lastCommunicationTimestamp: '2021-12-03T17:53:41.560939'
      currentJobID: 'currently running job ID or None if idle'