Add back the overrides loading at handler level as a fallback

To make the change non-breaking in case if other apps
used this handler which is a part of the public API

jupyterlab_server/settings_handler.py

@@ -25,7 +25,7 @@ def initialize(  # type:ignore[override]
         schemas_dir: str,
         settings_dir: str,
         labextensions_path: list[str],
-        overrides: dict[str, Any],
+        overrides: dict[str, Any] | None = None,
         **kwargs: Any,  # noqa: ARG002
     ) -> None:
         """Initialize the handler."""

jupyterlab_server/settings_utils.py

@@ -448,17 +448,24 @@ def initialize(
         schemas_dir: str,
         settings_dir: str,
         labextensions_path: list[str] | None,
-        overrides: dict[str, Any],
+        overrides: dict[str, Any] | None = None,
         **kwargs: Any,
     ) -> None:
         """Initialize the handler."""
         super().initialize(**kwargs)
+        error = None
+        if not overrides:
+            overrides, error = _get_overrides(app_settings_dir)
         self.overrides = overrides
         self.app_settings_dir = app_settings_dir
         self.schemas_dir = schemas_dir
         self.settings_dir = settings_dir
         self.labextensions_path = labextensions_path
 
+        if error:
+            overrides_warning = "Failed loading overrides: %s"
+            self.log.warning(overrides_warning, error)
+
     def get_current_locale(self) -> str:
         """
         Get the current locale as specified in the translation-extension settings.