[AAE-4966] Extensible app config (#6914)

* merge app config from the extensions

* improved service injection in unit tests

* extra unit test

* fix content tests

* update code as per review

* fix lint

* fix lint

* update code and tests

* update schema

lib/core/mock/alfresco-api.service.mock.ts

@@ -35,7 +35,7 @@ export class AlfrescoApiServiceMock extends AlfrescoApiService {
     initialize(): Promise<any> {
         return new Promise((resolve) => {
             this.alfrescoApiInitialized.next(true);
-            resolve();
+            resolve({});
         });
     }
 }