Add "Update the Control Plane" to Crosswalk guide

[clstokes]

Problem description

The Crosswalk guide covers nearly all aspects of k8s management, but a page covering "Update the Control Plane" seems to be missing.

Affected product version(s)

Suggestions for a fix

This likely falls to the individual provider implementations themselves (EKS, GKE, etc), but it would be good to provide an overview of this and then link to their appropriate guides and documentation.