Disallow the use of legacy addons

[hakman]

These are no longer maintained and kept around to not break very old versions of kOps.

/cc @olemarkus @johngmyers @rifelpet

[johngmyers]

This is more than just deprecating. This is removing.

[hakman]

This is more than just deprecating. This is removing.

Not quite removing, but disallowing the use. They have not been useable for some time.

[johngmyers]

1.22 is already deprecating the legacy metrics server and cluster server addons. I wouldn't mind extending that to some or all of the other legacy addons. But this should be announced in release notes and anything further should wait until 1.23 at the earliest.

[justinsb]

I agree with both of you (I think): this functionality probably is better done via another mechanism now, but we should do so carefully to avoid breaking anyone that might be using it!

[hakman]

I agree to with the feedback.
What do you think about disabling it based on k8s version, starting with k8s 1.23?

[hakman]

/retest

[olemarkus]

/lgtm

[k8s-ci-robot]

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