WebUI: Advanced download option

[fpiesche]

I frequently run into issues when downloading videos from non-youtube sites (eg. ZDF Mediathek) where youtube-dlp picks an audio track with audio description for sight impaired users over a regular one, forcing me to manually specify the formats to grab. This isn't an issue with your web UI or Docker image specifically but a general problem that youtube-dl and youtube-dlp can run into.

To accommodate this use case, a useful feature for the web UI would be an advanced download dialog that gets available formats for the given URL and allows the user to select the desired streams before starting the actual download.