fix rke2-helmchart-prevent-uninstall Kyverno policy (make it effective for MetalLB)

As @feleouet pointed out, the rke2-helmchart-prevent-uninstall Kyverno policy (introduced in !3271 (merged)), has a bug which prevents it from being applied to MetalLB: the policy defined in kube-system namespace, can't match the metallb RKE2 HelmChart defined in metallb-system.

This MR fixes this issue, which will allow this safeguard to be effective.

It seems nice to have it during the upgrade from 1.1.1, because in that scenario we still have old RKE2 nodes still having the static manifests for metallb HelmChart, and they might try a reinstallation of the Helm release, and might hit the corner case where they fail and fallback to uninstalling the chart).

(without !3347 (merged) the kube-system/calico/coredns part of this policy is only effective via the background controller -- this MR does not modify anything regarding this part)