[Housekeeping] Configure grpc_health_prob in admin

[yindia]

Describe the issue

Currently, flyteadmin doesn't have a health check prob in deployment. We need a health check prob for flyteadmin. We can use https://github.com/grpc-ecosystem/grpc-health-probe for running a health check

What if we do not do this?

It's best practice

Related component(s)

flyteadmin

Are you sure this issue hasn't been raised already?

• Yes

Have you read the Code of Conduct?

• Yes

[EngHabu]

1. We have installed grpc healthcheck in boilerplate Dockerfile template but it hasn't been applied to flyteadmin's Dockerfile.

2. Docs for gRPC liveness probes: this and this.

3. We should also add healthchecks for the REST endpoint