Add option to read in YouTube video as source

[nlitz88]

I think one of the earliest/fastest ways people will be able to adopt this or play around with it is to just feed it a recording of their stream from YouTube. Therefore, if it's just to test it out, then I should add support in the video-source argument for supplying a link to a YouTube video and grabbing frames from there.

Also, I'm pretty sure supervision has functions for enabling this, so I'm betting it's something we can add fairly quickly.

Also, a YouTube STREAM is really the big target!

OR, in the future, if this system ends up as a docker system--just include a container that serves as an RTMP server. Then, set it up so that your existing streaming device just sends video to that RTMPs server container. Still not as flexible as just sending it straight up to YouTube, so may have to consider some alternatives.

It looks like Ultralytics has an RTMP input source, as well as a YouTube link. Not sure if the YouTube option supports live streaming yet: https://docs.ultralytics.com/modes/predict/#inference-sources

If not, there's a library called "pafy" that some people recommend for working with YouTube content: https://pythonhosted.org/pafy/