Add support for NVIDIA AV1 support

[Proryanator]

Would be adding in AV1 encoding support for Nvidia GPUs. Depending on the quality results at the given resolutions/fps, we may want to relook at the VMAF quality setting to target.

The results of the Intel Arc AV1 encoding bitrates seem oddly close to Nvidia's NVENC H264, even though AV1 should be able to produce similar quality at much lower bitrates.

If the Nvidia AV1 encoder produces way better results (i.e. lower bitrate for same res@fps lossless encoding), we can keep the vmaf threshold as high as it is.

However, if the Nvidia encoder also seems to provide similar bitrates, we may want to revisit whether the vmaf target is too high.