🌱 Deprecate v1alpha6

[EmilienM]

What this PR does / why we need it:

Mark v1alpha6 version deprecated in our Kubernetes CRDs.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #1886

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[huxcrux]

I have no experience with how deprications have worked prior in CAPO however would it be beneficial to add information regarding deprecation and maybe a removal timeframe to docs or maybe even README?

Away from the above questions I think this pr looks good :)

[lentzi90]

I have no experience with how deprications have worked prior in CAPO however would it be beneficial to add information regarding deprecation and maybe a removal timeframe to docs or maybe even README?

Away from the above questions I think this pr looks good :)

Yes we should define a policy for how long we support older API versions and releases. I think we could basically copy CAPIs policy.

[lentzi90]

v1alpha7 has been around since v0.8 so I think this is reasonable
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: EmilienM, lentzi90

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[mdbooth]

/lgtm