add source code and readme

manifests/infrastructure/postgresql/postgresql-dashboard-metrics.yaml

@@ -0,0 +1,34 @@
+---
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: postgresql-dashboard-metrics
+  namespace: postgresql-system
+  labels:
+    app: postgresql-shared
+    cnpg.io/reload: ""
+data:
+  queries: |
+    # Simple replication lag metric
+    pg_replication_lag_seconds:
+      query: |
+        SELECT 
+          pg_stat_replication.application_name,
+          pg_stat_replication.client_addr,
+          pg_stat_replication.state,
+          COALESCE(EXTRACT(EPOCH FROM (now() - pg_stat_activity.query_start)), 0) AS lag_seconds
+        FROM pg_stat_replication
+        LEFT JOIN pg_stat_activity ON pg_stat_replication.pid = pg_stat_activity.pid
+      metrics:
+        - application_name:
+            usage: "LABEL"
+            description: "Application name of the standby"
+        - client_addr:
+            usage: "LABEL"
+            description: "IP address of the standby server"
+        - state:
+            usage: "LABEL"
+            description: "Current WAL sender state"
+        - lag_seconds:
+            usage: "GAUGE"
+            description: "Replication lag in seconds"