Add simplified PostgreSQL infrastructure role for database services

- Provides PostgreSQL server as shared database infrastructure
- Follows KISS principle with only essential configuration (11 variables vs 45 originally)
- Implements maximum security with Unix socket-only superuser access
- Uses scram-sha-256 authentication for application users
- Includes SystemD security hardening
- Applications manage their own databases/users via this infrastructure
- Production-ready with data checksums and localhost-only access

roles/postgresql/defaults/main.yml

@@ -0,0 +1,52 @@
+---
+# =================================================================
+# PostgreSQL Infrastructure Role - Simplified Configuration
+# =================================================================
+# Provides PostgreSQL database server as shared infrastructure
+# Applications manage their own databases/users
+
+# =================================================================
+# Essential Configuration
+# =================================================================
+
+# Service Management
+postgresql_service_enabled: true
+postgresql_service_state: "started"
+
+# Network Security (localhost only)
+postgresql_listen_addresses: "localhost"
+postgresql_port: 5432
+
+# Authentication
+postgresql_auth_method: "scram-sha-256"
+
+# Database Cluster Setup
+postgresql_encoding: "UTF8"
+postgresql_locale: "C.UTF-8"
+postgresql_data_checksums: true
+
+# Security
+postgresql_systemd_security: true
+
+# =================================================================
+# Optional Performance (Conservative Defaults)
+# =================================================================
+
+# Basic performance settings - PostgreSQL defaults are excellent
+postgresql_max_connections: 100
+postgresql_shared_buffers: "128MB"
+
+# =================================================================
+# Infrastructure Notes
+# =================================================================
+# This role provides minimal PostgreSQL infrastructure
+# Applications should create their own databases/users:
+#
+# - postgresql_user:
+#     name: myapp
+#     password: "{{ vault_myapp_password }}"
+# - postgresql_db:
+#     name: myapp
+#     owner: myapp
+#
+# PostgreSQL's built-in defaults are used for everything else