feat(web,server): link/unlink oauth account (#1154)

* feat(web,server): link/unlink oauth account

* chore: linting

* fix: broken oauth callback

* fix: user core bugs

* fix: tests

* fix: use user response

* chore: update docs

* feat: prevent the same oauth account from being linked twice

* chore: mock logger

mobile/openapi/test/user_response_dto_test.dart

@@ -61,6 +61,11 @@ void main() {
       // TODO
     });
 
+    // String oauthId
+    test('to test the property `oauthId`', () async {
+      // TODO
+    });
+
 
   });