ClusterClass: control plane template rotation leaks InfrastructureMachineTemplates

[sbueringer]

What steps did you take and what happened:

With ClusterClass, when a control plane InfrastructureMachineTemplate is rotated we don't delete the old template.

What did you expect to happen:
I expect old templates to be deleted - at least on a best effort basis.

Anything else you would like to add:

This can be reproduced by deploying a CAPD cluster with ClusterClass. After the initial deployment
the InfrastructureMachineTemplate of KCP must be modified to trigger rotations. This can be e.g. done
by changing the template referenced in the ClusterClass or changing fields via patches.

Environment:

• Cluster-api version: latest
• Minikube/KIND version:
• Kubernetes version: (use kubectl version):
• OS (e.g. from /etc/os-release):

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

/cc @fabriziopandini

[killianmuldoon]

/assign