[release-1.4] ✨ add support or concurrent MD upgrades in classy clusters

[k8s-infra-cherrypick-robot]

This is an automated cherry-pick of #8432

/assign fabriziopandini

[sbueringer]

@CecileRobertMichon @enxebre @vincepri @fabriziopandini @killianmuldoon

Hey folks,
as mentioned on Wednesday in the office hours we would like to cherry-pick this change which is an extension of the experimental ClusterClass feature.

Enhancements or additions to experimental Cluster API features, with the goal of allowing faster adoption and iteration; Please note that stability of the branch will always be top priority while evaluating those PRs, and thus approval requires /lgtm from at least two maintainers that, on top of checking that the backport is not introducing any breaking change for either API or behavior, will evaluate if the impact of those backport is limited and well-scoped e.g. by checking that those changes should not touch non-experimental code paths like utils and/or by applying other considerations depending on the specific PR.

• The change only affects ClusterClass, specifically the logic which calculates when a MachineDeployment is upgraded
• The default behavior (if the annotation is not set) is the same as before this change. I.e. this change is only active if a user explicitly adds the annotation

Please let us know if you have any objections. We would like to merge the cherry-pick ~ the week after KubeCon so it will be part of the v1.4.2 release.

[sbueringer]

/lgtm
/approve

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: 772671dfc0fdceccf3a22896a48a32e1924dc2fa

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: sbueringer

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