Add label to the CRD registered by KubePlus

[devdattakulkarni]

As part of registering the CRD defined in ResourceComposition, we should add a unique label to the CRD (say, registered-by:kubeplus). This will enable using the label selectors to query the CRDs registered by KubePlus easily using kubectl.

Example:
kubectl label crd atomicgggs.platformapi.kubeplus registered-by=kubeplus --kubeconfig=kubeplus-saas-provider.json

kubectl get crds -l registered-by=kubeplus --kubeconfig=kubeplus-saas-provider.json

NAME CREATED AT atomicgggs.platformapi.kubeplus 2024-01-05T11:55:46Z