Enforce compatibility for service deployment in MultiClusterService

[wahabmk]

Since the MultiClusterService object also uses the same ServiceTemplateSpec as ManagedCluster, should we enforce compatibility for service deployment on it as well?

Although we can't do it the way it is done for ManagedCluster in the admission webhooks as we can't know beforehand which clusters the MultiClusterService will match.

[zerospiel]

it could be checked within the mcs controller during the reconciliation, as it is now implemented in the template-ctrl (templates also cannot be checked in the validating webhook)