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

playbooks/add-postgres-to-prometheus.yml

@@ -0,0 +1,35 @@
+---
+- name: Add PostgreSQL exporter to Prometheus
+  hosts: 192.168.0.105
+  become: yes
+
+  tasks:
+    - name: Add postgres_exporter scrape config
+      blockinfile:
+        path: /etc/prometheus/prometheus.yml
+        insertafter: '  # Nginx metrics via nginx-prometheus-exporter'
+        block: |2
+          # PostgreSQL metrics via postgres_exporter
+          - job_name: 'postgres-app2'
+            scrape_interval: 15s
+            scrape_timeout: 10s
+            static_configs:
+              - targets: ['192.168.0.111:9187']
+                labels:
+                  instance: 'app2'
+                  service: 'postgresql'
+                  job: 'postgres'
+            metric_relabel_configs:
+              - source_labels: [__address__]
+                target_label: instance
+              - source_labels: [__address__]
+                regex: '([^:]+):\\d+'
+                replacement: '${1}'
+                target_label: host
+        marker: "# {mark} ANSIBLE MANAGED BLOCK - postgres_exporter"
+        backup: yes
+
+    - name: Reload Prometheus
+      systemd:
+        name: prometheus
+        state: reloaded