Ticket(s)

• Add liveness, readiness and startup probes to API #352

Description

This PR adds health check probes. All the probes return whether all the servers are running or not. The health check works both on the gRPC server and the HTTP server and can be tested using the following commands:

$ curl http://localhost:18080/healthz       
{"status":"SERVING"}
$ grpc-client-cli health localhost:19090 
{
 "status":  "SERVING"
}

Related PRs

N/A

Development Checklist

• I have added a descriptive title to this PR.
• I have squashed related commits together.
• I have rebased my branch on top of the latest main branch.
• I have performed a self-review of my own code.
• I have commented on my code, particularly in hard-to-understand areas.
• I have added docstring(s) and type annotations to my code.
• I have made corresponding changes to the documentation (docs).
• I have added tests for my changes.

Legal Checklist

• I have read the CONTRIBUTING document.
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• I have read and agreed to the Apache CLA (required).
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