Use a more specific selector than control-plane: controller-manager

[matthchr]

Describe the current behavior
We use the kubebuilder default selector control-plane: controller-manager, which many other projects may also use. We should be good citizens and at least in theory support being installed into the same namespace, but if we're using the same labels as other deployments webhooks and other selectors may get confused.

See #4274 as an example.

Describe the improvement
Use a label unique to ASO.

[matthchr]

The challenge here is that we have to delete the deployment in order to change this field.

We can do this with a Helm hook, but given it's a bit involved I'm going to kick this out to 2.11 for now.
See: https://github.com/giantswarm/azure-scheduled-events/pull/20/files for a simple example of what I'm talking about