🌱 MachinePool: automatically bump apiVersions like in our other controllers

[sbueringer]

Signed-off-by: Stefan Büringer buringerst@vmware.com

What this PR does / why we need it:
Today the MachinePool controller is our only controller that doesn't automatically bump the apiVersions in references.
This PR makes the controller consistent with our other controllers.

Please note, if infra or bootstrap providers (e.g. CABPK) drop api versions (like v1alpha3/v1alpha4) without this change existing MachinePools might break and manual user intervention is required.

Example:

1. MachinePool has been created with a reference to v1alpha3.KubeadmConfig
2. MachinePool controller doesn't bump the ref
3. Cluster API v1.x drops v1alpha3
4. MachinePool controller breaks as v1alpha3 doesn't exist anymore
5. User has to fix the MachinePool manually by upgrading the apiVersion

A comment about ref bumps in other controllers:

• works in: ClusterClass, Cluster, KCP, MS, Machine
• buggy in MD: will be fixed via: ⚠️ Remove PopulateDefaultsMachineDeployment and fix how MD controller set revision #7992
• not implemented in MP: will be fixed in this PR

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 #6778

[sbueringer]

/assign @CecileRobertMichon @fabriziopandini @killianmuldoon

[fabriziopandini]

Thanks for addressing this issue!
/lgtm

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: 277f7958dc31e018f4a9afa63783403af31cabce

[CecileRobertMichon]

/assign @Jont828 @mboersma

[sbueringer]

@killianmuldoon Can you please take a look if you have some time? The prod-code change is basically only to add the ref bump, everything else is adjusting the tests accordingly

Thank you very much!

[sbueringer]

I'll merge given lgtm above.

Please let me know if you have further comments. Happy to open a follow-up PR.

/approve

[k8s-ci-robot]

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[sbueringer]

/retest