prevent breaking mgmt cluster VIP

We need to ensure that the mgmt cluster VIP-related resources cannot be deleted:

  • cluster-vip Service
  • MetalLB lbpool IPAddressPool
  • MetalLB l2advertisement L2Advertisement

To achieve this, we need to:

  • set spec.prune: false on the related Kustomizations
  • set kustomize.toolkit.fluxcd.io/prune: disabled on cluster-vip Service
  • set Helm keep annotation (in metallb-resources)

/cc @feleouet @cristian.manda