kubernetes: document monitoring points for a cluster

[philips]

In a production configuration Kubernetes has a number of points that should be monitored. This document describes points that should be monitored externally and on-host. Doing this sort of monitoring is recommended to ensure long-term cluster health and availability.

This guide serves as an overview of what can be monitored and assumes knowledge of monitoring HTTPS based service.

WIP doc: https://docs.google.com/document/d/1jKwT2ymhvvV8Gflag8P2Y4JoCAPRY8vAyisecx2wJVc/edit#

[philips]

@fabxc could you perhaps help out on this?

[philips]

cc @kbrwn