feat(db): implement PostgreSQL monitoring and maintenance features

Added PostgreSQL monitoring and maintenance capabilities to the API, including new endpoints for instance-level metrics, maintenance operations, and job scheduling. Updated the HTTP API to support PostgreSQL monitoring routes and integrated a background scheduler for metrics collection. Enhanced the CLI with database commands for maintenance tasks. Updated documentation to reflect these changes.

migrations/postgres/000024_postgres_monitoring.down.sql

@@ -0,0 +1,2 @@
+DROP TABLE IF EXISTS postgres_maintenance_audit;
+DROP TABLE IF EXISTS postgres_monitor_snapshot;