adds variables EvalRequest is searching for

EvalRequest initialization fails when called with **data, because **data in this demo can include `base_model` and `private`.

src/backend/manage_requests.py

@@ -25,6 +25,8 @@ class EvalRequest:
     likes: Optional[int] = 0
     params: Optional[int] = None
     license: Optional[str] = ""
+    base_model: Optional[str] = ""
+    private: Optional[bool] = False
     
     def get_model_args(self):
         """Edit this function if you want to manage more complex quantization issues. You'll need to map it to