feat(server) user-defined storage structure (#1098)

[Breaking] newly uploaded file will conform to the default structure of `{uploadLocation}/{userId}/year/year-month-day/filename.ext`

mobile/openapi/test/system_config_dto_test.dart

@@ -26,6 +26,11 @@ void main() {
       // TODO
     });
 
+    // SystemConfigStorageTemplateDto storageTemplate
+    test('to test the property `storageTemplate`', () async {
+      // TODO
+    });
+
 
   });