feat: Add PostgreSQL support for Gitea installer

- Add PostgreSQL configuration options
- Generate PostgreSQL YAML when selected
- Verify PostgreSQL pod readiness
- Update documentation for PostgreSQL usage
- Add PostgreSQL service and pod definitions

lib/installers/k8s/gitea/templates/postgres.yaml

@@ -0,0 +1,56 @@
+apiVersion: v1
+kind: PersistentVolumeClaim
+metadata:
+  name: postgres-data
+  namespace: @{config_values.namespace}
+spec:
+  accessModes: [ReadWriteOnce]
+  resources:
+    requests:
+      storage: @{config_values.storage_size}
+---
+apiVersion: v1
+kind: Pod
+metadata:
+  name: @{config_values.db_host}
+  namespace: @{config_values.namespace}
+  labels:
+    app: @{config_values.db_host}
+spec:
+  containers:
+  - name: postgres
+    image: postgres:16-alpine
+    env:
+    - name: POSTGRES_DB
+      value: @{config_values.db_name}
+    - name: POSTGRES_USER
+      value: @{config_values.db_user}
+    - name: POSTGRES_PASSWORD
+      value: @{config_values.db_password}
+    - name: PGDATA
+      value: /var/lib/postgresql/data/pgdata
+    ports:
+    - containerPort: 5432
+      name: postgres
+    volumeMounts:
+    - name: postgres-storage
+      mountPath: /var/lib/postgresql/data
+  volumes:
+  - name: postgres-storage
+    persistentVolumeClaim:
+      claimName: postgres-data
+---
+apiVersion: v1
+kind: Service
+metadata:
+  name: @{config_values.db_host}
+  namespace: @{config_values.namespace}
+spec:
+  selector:
+    app: @{config_values.db_host}
+  ports:
+  - port: 5432
+    targetPort: 5432
+    name: postgres
+  type: ClusterIP
+