Add ability to select GPU for ffmpeg (#20455)

* Add ability to set selected GPU for ffmpeg

* Cleanup

* Cleanup

* Improve handling

frigate/config/camera/ffmpeg.py

@@ -67,6 +67,7 @@ class FfmpegConfig(FrigateBaseModel):
         default=False,
         title="Set tag on HEVC (H.265) recording stream to improve compatibility with Apple players.",
     )
+    gpu: int = Field(default=0, title="GPU index to use for hardware acceleration.")
 
     @property
     def ffmpeg_path(self) -> str: