Enable creating kubeadm and RKE2 cluster in CAPZ

[alexander-demicev]

There is a problem at the moment with CAPZ, it's only able to watch one type of bootstrap config object https://github.com/kubernetes-sigs/cluster-api-provider-azure/blob/main/main.go#L259, this makes it impossible running 2 bootstrap providers at the same time if users are utilizing machine pools.

[furkatgofurov7]

The problem and corresponding flag was introduced to fix rancher/turtles#483 where the controller was exclusively watching Kubeadm resources and not allowing the use of any other bootstrap provider. It is interesting use case though, I am curious if any other infra providers support such a use case and how they handle it.