Add Azure kubeadm ClusterClass example

[anmazzotti]

Currently the only flavor tested and published is using RKE2.
It would be nice to add a kubeadm flavor to the examples and cover it in e2e test as well.
This could highlight whether a test failure is infrastructure provider related or not, and highlight issues that are not present in RKE2 but in kubeadm, or the other way around, for comparison.