Provide monitor information also through event bus API

[mcweba]

The current implementation provides the monitor information through the HTTP API by calling

GET /queuing/monitor

this results in a json response like this:

{
  "queues": [
    {
      "name": "queue_1",
      "size": 3
    },
    {
      "name": "queue_2",
      "size": 2
    }
  ]
}

With this issue we want to introduce this API endpoint also through the event bus API.

The request object could look something like this:

{
    "operation": "monitor",
    "payload": {
        "emptyQueues": <boolean value to define whether to include empty queues or not>,
        "limit": <limit the amount of queues to return>
    }
}