[ResponseOps][MaintenanceWindows] Fix mw internal client by passing hidden SO type (elastic#248132)

## Summary

Internal MW client using internal repository was introduced in
elastic#247390.
It created problems while fetching MWs using all spaces in synthetics
plugin.

This PR fixes the issue.

### Checklist

Check the PR satisfies following conditions. 

Reviewers should verify this PR satisfies this list as well.

- [x] Review the [backport
guidelines](https://docs.google.com/document/d/1VyN5k91e5OVumlc0Gb9RPa3h1ewuPE705nRtioPiTvY/edit?usp=sharing)
and apply applicable `backport:*` labels.

Author: js-jankisalvi

x-pack/platform/plugins/shared/maintenance_windows/server/maintenance_window_client_factory.test.ts

@@ -107,12 +107,16 @@ test('creates an internal maintenance window client', async () => {
   const factory = new MaintenanceWindowClientFactory();
   factory.initialize(maintenanceWindowClientFactoryParams);
   const request = mockRouter.createKibanaRequest();
-  const mockRepository = savedObjectsService.createInternalRepository();
+  const mockRepository = savedObjectsService.createInternalRepository([
+    MAINTENANCE_WINDOW_SAVED_OBJECT_TYPE,
+  ]);
   savedObjectsService.createInternalRepository.mockReturnValue(mockRepository);
 
   factory.createInternal(request);
 
-  expect(savedObjectsService.createInternalRepository).toHaveBeenCalledWith();
+  expect(savedObjectsService.createInternalRepository).toHaveBeenCalledWith([
+    MAINTENANCE_WINDOW_SAVED_OBJECT_TYPE,
+  ]);
 
   const { MaintenanceWindowClient } = jest.requireMock('./client');