Add metrics-server Kubernetes addon

[kayrus]

Kubernikus clusters don't support kubectl top pod:

kubectl top pod
Error from server (NotFound): the server could not find the requested resource (get services http:heapster:)

https://github.com/kubernetes-sigs/metrics-server#deployment

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.