chore: Update some type hints in config. (#5833)

api/configs/app_config.py

@@ -8,6 +8,9 @@ from configs.middleware import MiddlewareConfig
 from configs.packaging import PackagingInfo
 
 
+# TODO: Both `BaseModel` and `BaseSettings` has `model_config` attribute but they are in different types.
+# This inheritance is depends on the order of the classes.
+# It is better to use `BaseSettings` as the base class.
 class DifyConfig(
     # based on pydantic-settings
     BaseSettings,