etcd-client starts retrying transient errors from the etcd cluster
etcd-client starts retrying transient errors from the etcd cluster

This PR enables unaryClientInterceptor in conjunction with Prometheus interceptor.
Previously it was simply overwritten by the Prometheus interceptor.
As a result etcd client didn't attempt to retry certain errors.

The unaryClientInterceptor is important because it knows how to retry all sorts of errors from the etcd cluster. It will make the API server more resilient to failures -  end users won't see certain errors.
The full list of retriable (codes.Unavailable) errors can be found at https://github.com/etcd-io/etcd/blob/main/api/v3rpc/rpctypes/error.go#L72

Kubernetes-commit: 83171562b0954b2e19eb69943f01a44779cc7a8f

kubernetes/apiserver,kubernetes/apiserver