feat(db): batch cleanup expired rows from postgres

### Summary

The PR #10405 changed cleanup to only happen on nodes that have Admin API listeners.

This PR makes deletion to happen in maximum of 50.000 row batches.

Inspired from #10331 and #10389.

CHANGELOG.md

@@ -100,6 +100,7 @@
 #### Core
 
 - Postgres TTL cleanup timer will now only run on traditional and control plane nodes that have enabled the Admin API.
+- Postgres TTL cleanup timer now deletes maximum of 50.000 rows per table per cleanup round.
 
 ## 3.2.0
 

kong/db/strategies/postgres/connector.lua

@@ -325,13 +325,17 @@ function _mt:init_worker(strategies)
       local table_name = table_names[i]
       local column_name = table_name == "cluster_events" and expire_at_escaped
                                                           or ttl_escaped
-      cleanup_statements[i] = concat {
-        "  DELETE FROM ",
-        self:escape_identifier(table_name),
-        " WHERE ",
-        column_name,
-        " < CURRENT_TIMESTAMP AT TIME ZONE 'UTC';"
-      }
+      local table_name_escaped = self:escape_identifier(table_name)
+
+      cleanup_statements[i] = fmt([[
+    WITH rows AS (
+  SELECT ctid
+    FROM %s
+   WHERE %s < CURRENT_TIMESTAMP AT TIME ZONE 'UTC'
+ORDER BY %s LIMIT 50000 FOR UPDATE SKIP LOCKED)
+  DELETE
+    FROM %s
+   WHERE ctid IN (TABLE rows);]], table_name_escaped, column_name, column_name, table_name_escaped)
     end
 
     local cleanup_statement = concat(cleanup_statements, "\n")