feat: add PostgreSQL infrastructure for App2

- Add PostgreSQL role for installing and configuring PostgreSQL 17
- Add postgres_exporter role for PostgreSQL metrics collection
- Add deploy-postgres-app2.yml playbook for deployment
- Configure test database 'testdb' with user 'testuser'
- Set up postgres_exporter user for monitoring
- Include firewall configuration for PostgreSQL (5432) and postgres_exporter (9187)
- Follow existing role structure pattern from node_exporter

roles/postgres_exporter/defaults/main.yml

@@ -0,0 +1,12 @@
+---
+# Postgres Exporter
+postgres_exporter_version: "0.15.0"
+postgres_exporter_port: 9187
+postgres_exporter_user: "postgres_exporter"
+postgres_exporter_password: "exporterpassword123"
+
+# Connection settings
+postgres_exporter_data_source_name: "user={{ postgres_exporter_user }} password={{ postgres_exporter_password }} host=localhost port=5432 dbname=postgres sslmode=disable"
+
+# Systemd service
+postgres_exporter_service_name: "postgres_exporter"