Implement support for YOLOv9 via ONNX (#16459)

* WIP yolov9

* Implement post processing for yolov9

* Cleanup detection

* Update docs to make note of supported yolov9

* Move post processing to separate utility

* Add note about other models

frigate/detectors/detector_config.py

@@ -35,6 +35,7 @@ class InputDTypeEnum(str, Enum):
 class ModelTypeEnum(str, Enum):
     ssd = "ssd"
     yolox = "yolox"
+    yolov9 = "yolov9"
     yolonas = "yolonas"