CPMS assumes diff on empty zone in Azure

When we merged https://github.com/openshift/cluster-control-plane-machine-set-operator/pull/229, it changed the way failure domains were injected for Azure so that additional fields could be accounted for. However, the CPMS failure domains have Azure zones as a string (which they should be) and the machine v1beta1 spec has them as a string pointer.

This means now that the CPMS is detecting the difference between the a nil zone and an empty string, even though every other piece of code in openshift treats them the same.

We should update the machine v1beta1 type to remove the pointer. This will be a no-op in terms of the data stored in etcd since the type is unstructured anyway.

It will then require updates to the MAPZ, CPMS, MAO and installer repositories to update their generation.

4.14 nightlies from the merge of 229 onwards

This is only affecting regions in Azure where there are no zones, currently in CI it's affecting about 20% of events.

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