Fix LPR vehicle message for multiple models (#24119)

* use the camera's model for the lpr vehicle check

`FrigateConfig.model` became `models[]` in the detector refactor, so this didn't compile on 0.19. Each camera has its own detector/model pair now, so the check resolves the camera's scene with `getModelForCamera` instead of looking at every model.

* use camera config model

* fix export test

frigate/camera/state.py

@@ -63,7 +63,7 @@ class CameraState:
         self.lpr_min_obj_area: int = 0
         self.lp_objects = {
             label
-            for label, attributes in config.model.attributes_map.items()
+            for label, attributes in self.model.attributes_map.items()
             if "license_plate" in attributes
         }