docs: Add example manifests for common deployment patterns

[josedab]

Description

Add ready-to-use example YAML files for common deployment scenarios.

Task

• Create examples/ directory with:
  • minimal-cluster.yaml (1 replica, no TLS)
  • production-cluster.yaml (3 replicas, TLS, anti-affinity)
  • topic-with-retention.yaml
  • user-with-acls.yaml
• Add links to these examples from the README

Helpful Context

• See the CRD definitions in src/crd/ for available fields