Cache for Helix rest - Zk read intensive APIs

[xyuanlu]

Is your feature request related to a problem? Please describe. Helix-rest apis like stoppable and partition assignment reads the whole cluster's info every time. When these APIs are called multiple times in a short period of time, it will cause massive read traffic to ZK.

Describe the solution you'd like We would like to have a rest cache that are updated based on event. (just like controllerDataProvider)

Additional context Add any other context or screenshots about the feature request here.