GKE rule: Network policy and cluster sizing (BP)

[schweikert]

Doc: https://cloud.google.com/kubernetes-engine/docs/how-to/network-policy#limitations_and_requirements

If Network Policy is enabled, fail a best practice rule if the nodes are f1-micro or g1-small or if there are less than 3 nodes.

[eugenenuke]

This was implemented in 44b1e8e78abf0310013b5079052117321cecbafa