Use -aom-params lossless=1 with ffmpeg to get lossless AV1

There was a bug that makes the first frame if using -cfr 0 not lossless. But now, with that option it is lossless video! Fixed in https://git.videolan.org/?p=ffmpeg.git;a=commitdiff;h=288ca1c66740640d5742f2921efbf502d83f8b6a

For example it may be a good idea to reencode some of the lossless samples in https://archive.org/details/AV-LOSSLESS-TEST-MATERIAL and https://media.xiph.org/