## Why are these changes needed?
As in this https://github.com/ray-project/ray/pull/26405 we added the health check for gcs and raylets.
This PR expose them in the endpoint in dashboard and dashboard agent.
For dashboard, we added `http://host:port/api/gcs_healthz` and it'll send RPC to GCS directly to see whether the GCS is alive or not.
For agent, we added `http://host:port/api/local_raylet_healthz` and it'll send RPC to GCS to check whether raylet is alive or not.
We think raylet is live if
- GCS is dead
- GCS is alive but GCS think the raylet is dead
If GCS is dead for more than X seconds (60 by default), raylet will just crash itself, so KubeRay can still catch it.