torchcodec-xpu: define list of supported FFmpeg versions for Linux

[dvrogozh]

To optimize user experience for the torchcodec XPU plugin we need to define the list of FFmpeg versions we support. Different FFmpeg versions might support different codecs - this needs to be documented.

CC: @eromomon

[dvrogozh]

Decoders support by ffmpeg-vaapi:

Codec	FFmpeg version
AV1	n4.4
H.264	n0.10
H.265	n2.8
VP8	n4.0
VP9	n3.0
MJPEG	n4.0

Encoding support by ffmpeg-vaapi:

Codec	FFmpeg version
AV1	n6.1
H.264	n3.1
H.265	n3.1
VP8	n3.3
VP9	n3.4
MJPEG	n3.1

[dvrogozh]

ffmpeg versions in Ubuntu:

Ubuntu	ffmpeg
22.04	4.4.2
24.04	6.1.1
26.04	8.0.1