nvmeof: use .nvmeof pool for gateway and remove pool field from CRD

Changes:
- Use a dedicated .nvmeof pool (via CephBlockPool CR named
  builtin-nvmeof) for the NVMe-oF gateway internal state.
- Use a separate nvmeof pool for the StorageClass data.
- Remove the pool field from the CephNVMeOFGateway CRD.
  The gateway now always uses the .nvmeof pool, hardcoded
  in the operator.
- Add .nvmeof to the allowed CephBlockPool name overrides.
- Create a production example nvmeof.yaml (instances: 2,
  replicas: 3) and a CI-only nvmeof-test.yaml (instances: 1,
  replicas: 1).
- Update documentation and CI test script accordingly.

Signed-off-by: Oded Viner <oviner@redhat.com>
(cherry picked from commit ec502c3f80)

tests/scripts/github-action-helper.sh

@@ -1056,6 +1056,7 @@ function test_csi_nvmeof_workload {
   wait_for cephblockpool nvmeof rook-ceph 600
 
   kubectl create -f "${REPO_DIR}/deploy/examples/nvmeof-test.yaml"
+  wait_for cephblockpool builtin-nvmeof rook-ceph 600
   wait_for cephnvmeofgateway nvmeof rook-ceph 600
   timeout 300 bash <<EOF
 until kubectl -n rook-ceph get pod --no-headers 2>/dev/null | awk '/rook-ceph-nvmeof-nvmeof-a-/ && \$3 == "Running" {f=1} END {exit !f}'; do