MachineDeployment history should also track in-place propagating changes

What would you like to be added (User Story)?

As a user I would like track changes to a MachineDeployment in the MD's history. Currently on changes that cause a rollout are captured in the history (as separate MachineSets). As a user I would like MachineDeployment to also track changes to in-place propagating fields.

Detailed Description

Changes to some of the in-place propagating fields could change the properties of the underlying nodes. Example: changes to MachineDeployment.Spec.Template.Lables could change the labels on the underlying nodes.

Therefore it would be nice to be able to capture these changes in MachineDeployment history so that as a user I can rollback to the previous state, using clusterctl alpha rollout undo if necessary.

Anything else you would like to add?

Additional context:

This will primarily benefit classic clusters. For classy clusters, it is not currently possible to rollback to a previous state using clusterctl as the MachineDeployment is managed by cluster topology.

Label(s) to be applied

/kind feature One or more /area label. See https://github.com/kubernetes-sigs/cluster-api/labels?q=area for the list of labels.