[CN-1148] Add operator UCN tutorial (#371)

# Description of change

Please write a summary of your changes and why you made them. Be sure to
reference any related issues by adding `fixes #(issue)`.

## Type of change

Select the type of change that you're making:

- [ ] Bug fix (Addresses an issue in existing content such as a typo)
- [x] Enhancement (Adds new content)

## Open Questions and Pre-Merge TODOs
- [ ] Use github checklists to create a list. When an item is solved,
check the box and explain the answer.

antora-playbook-local.yml

@@ -179,6 +179,9 @@ content:
     - url: https://github.com/hazelcast-guides/hazelcast-platform-operator-tls
       branches: master
       start_path: docs
+    - url: https://github.com/hazelcast-guides/hazelcast-platform-operator-user-code-namespace
+      branches: master
+      start_path: docs
     - url: https://github.com/hazelcast-guides/kafka-kerberos
       branches: master
       start_path: docs

antora-playbook.yml

@@ -181,6 +181,9 @@ content:
     - url: https://github.com/hazelcast-guides/hazelcast-platform-operator-tls
       branches: master
       start_path: docs
+    - url: https://github.com/hazelcast-guides/hazelcast-platform-operator-user-code-namespace
+      branches: master
+      start_path: docs 
     - url: https://github.com/hazelcast-guides/kafka-kerberos
       branches: master
       start_path: docs