[FeatureRequest] Monitoring metrics for supervisors status

[layoaster]

Description

Currently, there is no way of monitoring the state of supervisors' health via monitoring metrics.

I would like to request a metric (or set of metrics) to report the following:

• Supervisor health status: whether a supervisor is healthy or not. (Druid API).
• Supervisor current state/status: e.g.: RUNNING, SUSPENDED, etc ... (List of possible states)

Motivation

• To be able to monitor the status of Druid supervisors via monitoring metrics.
• Supervisor is a critical piece of Druid when performing streaming ingestion.