processors/download_media: allow capping download resolution

[nodiscc]

• https://superuser.com/questions/1804254/how-to-select-maximum-resolution-and-specify-a-format-codec-in-yt-dlp
• https://github.com/yt-dlp/yt-dlp#filtering-formats

yt-dlp -v -f "bv*[height<=720][ext=mp4]+ba*[ext=m4a]" -N 4 "https://www.youtube.com/xxx"