[Feature request] FCast Support

[shellster]

I frequently use the mobile play feature in invidious to play videos. I know invidious is primarily focused on YouTube. However there was the recent development of the GrayJay app for viewing creators across services. More exciting to me, they also released an open source protocol and app called FCast which is an attempt at Airplay/Chromecast without the closed wall garden. The protocol is very simple and clearly designed primarily for DASH/HLS/MP4 video streams. I think it would be really handy to support FCast even if it were restricted to YouTube videos. The protocol will basically hand you the video link so it should be fairly simple to do the normal invidious YouTube man in the middle. The net result would be natural GrayJay integration and easier casting capabilities as more things support FCast.

https://fcast.org/