feat: add advisory_lock context manager (#283)

docs/reference/db.md

@@ -7,6 +7,7 @@ You can import them directly from `fastapi_toolsets.db`:
 ```python
 from fastapi_toolsets.db import (
     LockMode,
+    advisory_lock,
     cleanup_tables,
     create_database,
     create_db_dependency,
@@ -30,6 +31,8 @@ from fastapi_toolsets.db import (
 
 ## ::: fastapi_toolsets.db.lock_tables
 
+## ::: fastapi_toolsets.db.advisory_lock
+
 ## ::: fastapi_toolsets.db.wait_for_row_change
 
 ## ::: fastapi_toolsets.db.create_database