feat(server) Extend PUT /album/:id/assets endpoint (#857)

* Add new query parameter to API endpoint that allows adding assets to albums which potentially contain assets that are already part of this album.

* Change API endpoint

* Generate new APIs

* Fixed test

Co-authored-by: Alex Tran <alex.tran1502@gmail.com>

mobile/openapi/test/add_assets_response_dto_test.dart

@@ -0,0 +1,37 @@
+//
+// AUTO-GENERATED FILE, DO NOT MODIFY!
+//
+// @dart=2.12
+
+// ignore_for_file: unused_element, unused_import
+// ignore_for_file: always_put_required_named_parameters_first
+// ignore_for_file: constant_identifier_names
+// ignore_for_file: lines_longer_than_80_chars
+
+import 'package:openapi/api.dart';
+import 'package:test/test.dart';
+
+// tests for AddAssetsResponseDto
+void main() {
+  // final instance = AddAssetsResponseDto();
+
+  group('test AddAssetsResponseDto', () {
+    // int successfullyAdded
+    test('to test the property `successfullyAdded`', () async {
+      // TODO
+    });
+
+    // List<String> alreadyInAlbum (default value: const [])
+    test('to test the property `alreadyInAlbum`', () async {
+      // TODO
+    });
+
+    // AlbumResponseDto album
+    test('to test the property `album`', () async {
+      // TODO
+    });
+
+
+  });
+
+}