Add support for piped as a backend source

[lordkitsuna]

This would be awesome as an alternative frontend to a https://github.com/teampiped/piped instance. It has an api and is used by apps like https://github.com/libre-tube/LibreTube.

The main benefit of this is that piped does the proxying itself on the instance and thus i can host my own to avoid overloaded public instances of things like invidious that tend to be painfully slow.

[opensourcecheemsburgers]

I have thought about this myself and it would be a nice addition. However, I do not have the time to write a piped-rs library and integrate it with RustyTube.