🐛Add DeleteMachineAnnotation for MachineSet Delete Policy

[wfernandes]

What this PR does / why we need it:
This PR adds another annotation called DeleteMachineAnnotation=cluster.x-k8s.io/delete-machine to the MachineSet Delete Policy because that annotation is the one that is documented.

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 #2912

Release Notes

• ➕ Add controllers.DeleteMachineAnnotation with value cluster.x-k8s.io/delete-machine. Please use this annotation moving forward as the other annotation DeleteNodeAnnotation is planned for removal in the next CAPI release.

[vincepri]

Code changes look good, deprecation warning should be there as @benmoss suggested

/milestone v0.3.4

[fabriziopandini]

LGTM for me as well.
Thanks @wfernandes!

[ncdc]

While we're in here - the code currently requires a non-empty string for the annotation's value. Should we change to a presence check?

[detiber]

While we're in here - the code currently requires a non-empty string for the annotation's value. Should we change to a presence check?

+1 from me

[wfernandes]

While we're in here - the code currently requires a non-empty string for the annotation's value. Should we change to a presence check?

Thanks for bringing this up. I thought that was weird too and wanted to bring that up. I'll fix it to make it a presence check instead.

[vincepri]

Changes LGTM

[vincepri]

/approve

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[wfernandes]

@vincepri Do we have an issue created to remove DeleteNodeAnnotation? If not, should we create one and mark it for the Next milestone?
Asking because I'm not sure how we track things that are marked for deprecation.

[vincepri]

Yes please, we can put it in v0.4

[detiber]

/lgtm