Add a resource for deploying the Kubernetes metrics-server

[ananace]

Currently, the cluster lacks the default metrics-server, a component that should be reasonably simple to deploy in a similar manner to CoreDNS/Flannel/etc - it shouldn't require any particular configuration apart from the defaults after all.

The project manifests as provided should map 1:1 to kubectl_apply calls, including the podAntiAffinity from the high-availability component - and potentially also the PodDisruptionBudget if the user requests multiple replicas.