Expose cluster versions and capabilities to templating steps

[joe-kimmel-vmw]

Describe the problem/challenge you have
see design proposal doc: https://hackmd.io/6FQhzRIPR_uceqtTqSIXaA

Describe the solution you'd like
per proposal doc, add to both Helm template specifically and ytt/cue templaters more generally

Anything else you would like to add:
[Additional information that will assist in solving the issue.]

Helm shouldn't be talking to the cluster; we should be talking the cluster and passing through things to helm.

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