Apply a label to all manifests generated by this repository

Add the `nerc.mghpcc.org/kustomized` label to all resources generated
by our overlays.

This makes it easy to identify things that we have either created or
modified (e.g., we can ask `kubectl get clusterrolebindings -l
nerc.mghpcc.org/kustomized`).

cluster-scope/overlays/nerc-ocp-infra/kustomization.yaml

@@ -1,5 +1,7 @@
 apiVersion: kustomize.config.k8s.io/v1beta1
 kind: Kustomization
+commonLabels:
+  nerc.mghpcc.org/kustomized: "true"
 resources:
 - ../common
 - ../../bundles/openshift-gitops