feat: add standalone keycloak helm chart with pgvector dependency

[skattoju]

Summary

This PR adds a standalone Keycloak Helm chart to the repository, following the established repository structure and patterns.

Changes

• ✅ Restructured keycloak chart to follow repository pattern (keycloak/helm/)
• ✅ Updated pgvector dependency to version 0.5.1 (matching current pgvector version)
• ✅ Added condition for optional pgvector deployment
• ✅ Updated all documentation and installation paths
• ✅ Added keycloak to main README with usage examples
• ✅ Chart includes dedicated pgvector PostgreSQL instance for Keycloak

Key Features

• Standalone deployment - No operator required
• Built-in database - Includes pgvector PostgreSQL subchart (optional, can use external DB)
• OpenShift & Kubernetes - Supports both Routes and Ingress
• Production-ready - Health checks, metrics, security contexts
• Flexible configuration - Extensive values.yaml options

Usage

Standalone Installation

helm install keycloak ./keycloak/helm \
  --namespace keycloak \
  --set admin.password=changeme \
  --set pgvector.secret.password=changeme

As Dependency

dependencies:
  - name: keycloak
    version: "1.0.0"
    repository: "file://../ai-architecture-charts/keycloak/helm"

Notes

This is a standalone Keycloak chart that does not require any operators. It uses the official Keycloak container images and includes an optional pgvector PostgreSQL subchart for the database backend.