Add support for new checkpointer statistics for PostgreSQL.

Introduced logic to check the existence of `pg_stat_checkpointer` and fetch corresponding statistics when available. This ensures compatibility with newer PostgreSQL versions while maintaining backward support using `pg_stat_bgwriter`.

backend/app/services/overview_collector.py

@@ -106,12 +106,31 @@ async def collect_overview(
         errors,
         "pg_stat_database_perf",
     )
-    bgwriter = await _safe_fetchrow(
+    checkpointer_view_exists = await _safe_fetchval(
         conn,
-        "SELECT checkpoints_timed, checkpoints_req FROM pg_stat_bgwriter",
+        "SELECT to_regclass('pg_catalog.pg_stat_checkpointer') IS NOT NULL",
         errors,
-        "pg_stat_bgwriter",
+        "checkpointer_view_exists",
     )
+    if checkpointer_view_exists:
+        bgwriter = await _safe_fetchrow(
+            conn,
+            """
+            SELECT
+              num_timed AS checkpoints_timed,
+              num_requested AS checkpoints_req
+            FROM pg_stat_checkpointer
+            """,
+            errors,
+            "pg_stat_checkpointer",
+        )
+    else:
+        bgwriter = await _safe_fetchrow(
+            conn,
+            "SELECT checkpoints_timed, checkpoints_req FROM pg_stat_bgwriter",
+            errors,
+            "pg_stat_bgwriter",
+        )
     autovac_workers = await _safe_fetchval(
         conn,
         """