Add support for ManagedClusterSet labeling when creating ClusterPools

[gurnben]

Summary of Request

ACM 2.3 adds support for ManagedClusterSets that allow you to federate access to ClusterPools, ClusterDeployments, and ClusterClaims. It also adds admission requirements for non-admin users to place their ClusterPool into a ManagedClusterSet, so its important that we support adding ClusterPools and Deployments at create time to a ManagedClusterSet.

I would suggest that we add an optional parameter to the create command for ClusterDeployments and ClusterPools, something like --cluster-set/-cs that allows you to provide a ManagedClusterSet name. That parameter will be translated into a label in the .metadata.labels list in the ClusterPool or ClusterDeployment YAML to apply.

The label in question should be added to .metadata.labels with the key:value pair cluster.open-cluster-management.io/clusterset:<MANAGEDCLUSTERSET_NAME>.