Saved object export: apply export hooks to referenced / nested objects (

elastic#100769)

* execute export transform for nested references

* fix sort

* fix duplicate references

* add FTR test

src/core/server/saved_objects/export/collect_exported_objects.test.mocks.ts

@@ -0,0 +1,12 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0 and the Server Side Public License, v 1; you may not use this file except
+ * in compliance with, at your election, the Elastic License 2.0 or the Server
+ * Side Public License, v 1.
+ */
+
+export const applyExportTransformsMock = jest.fn();
+jest.doMock('./apply_export_transforms', () => ({
+  applyExportTransforms: applyExportTransformsMock,
+}));