Druid Supervisors: What Do They Know? Do They Know Things?? Let's Find Out!

[vogievetsky]

It would be very useful if the Druid supervisors reported their internal status in their status API.

Legend has it that the supervisor knows more about its internal status than it is letting on, specifically when a supervisor has no tasks (and is not shutdown) it would return something like:

{
  "id": "wiki7",
  "generationTime": "2018-03-27T00:11:22.517Z",
  "payload": {
    "dataSource": "wiki7",
    "stream": "wikiticker",
    "partitions": 2,
    "replicas": 1,
    "durationSeconds": 3600,
    "activeTasks": [],
    "publishingTasks": []
  }
}

would be cool to surface the internal status "starting-up", "struck", e.t.c that made it have no tasks - it knows.