enable the management-cluster-only Kyverno policies component only in mgmt cluster

I noticed by chance (while doing !2150 (merged)) that !1773 (merged) wasn't doing one thing that it intended to do, or rather that the change done at the time was effective but isn't now that we enable Kyverno in bootstrap cluster and workload clusters.

This MR should ensure that the Kyverno policies specific to the mgmt cluster are only enabled in the mgmt cluster.

/cc @bogdan.antohe