Upgrade JetStack Cert-Manager to v0.15.2 (#6414)

* Upgrade JetStack Cert-Manager to v0.15.2

* Add README.md table of contents

roles/kubernetes-apps/ingress_controller/cert_manager/templates/clusterissuer-cert-manager.yml.j2

@@ -0,0 +1,23 @@
+# Copyright YEAR The Jetstack cert-manager contributors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+---
+apiVersion: cert-manager.io/v1alpha2
+kind: ClusterIssuer
+metadata:
+  name: ca-issuer
+  namespace: {{ cert_manager_namespace }}
+spec:
+  ca:
+    secretName: ca-key-pair