[`firestartr-bootstrap`] Add gatekeeper constrain to avoid deletion of customer namespaces

[alambike]

Motivation

We need to add a new Gatekeeper constrain when new customer is added, to firestartr-pro/state-sys-services repository, to avoid deletions of customer namespaces.

This constrain should have the following format:

apiVersion: constraints.gatekeeper.sh/v1beta1
kind: K8sBlockNamespaceDelete
metadata:
  name: block-<CUSTOMER>-ns-delete
spec:
  enforcementAction: deny
  match:
    kinds:
      - apiGroups: [""]
        kinds: ["Namespace"]
  parameters:
    protectedPrefix:
      - "<CUSTOMER>-"

See https://github.com/firestartr-pro/state-sys-services/pull/180/changes