feat(server): random assets API (#4184)

* feat(server): get random assets API

* Fix tests

* Use correct validation annotation

* Fix offset use in query

* Update API specs

* Fix typo

* Random assets e2e tests

* Improve e2e tests

mobile/openapi/test/asset_api_test.dart

@@ -112,6 +112,11 @@ void main() {
       // TODO
     });
 
+    //Future<List<AssetResponseDto>> getRandom({ num count }) async
+    test('test getRandom', () async {
+      // TODO
+    });
+
     //Future<List<TimeBucketResponseDto>> getTimeBuckets(TimeBucketSize size, { String userId, String albumId, String personId, bool isArchived, bool isFavorite, String key }) async
     test('test getTimeBuckets', () async {
       // TODO