API server auth

[IceKhan13]

What is the expected behavior?

Add authentication to KubeRay API server.

As API server is a simple HTTP endpoint we can probably reuse same sidecar proxy here too #137

Epic #105

[akihikokuroda]

The kuberay api-server helm chart doesn't have a hook for the side car container. It is not managed by any operator so the deployment can be patched during install for now. I'll work to create a PR in the kuberay repo to add the hook into the helm chart.

[akihikokuroda]

I created a PR updating the helm chart of the apiserver for the sidecar in Kuberay. ray-project/kuberay#920

[akihikokuroda]

I'm going to enable "Client Credentials Grant" in OAuth2 specification for the apiserver.