Add Invidious as an optional YouTube Source

Invidious is a clone of YouTube created for a similar reason to NewPipe. This site happens to use the exact same URL scheme as YouTube does, with pretty much the exact same layout, but with two major changes.

• Only Content
• More Information about Content

The only information that gets loaded on an Invidious page, is content and information about it. There is also slightly more information availible about the video loaded as well. I believe that invidious could be ported to NewPipe very quickly because of the way it is setup.

Here's an example video from Kurzgesagt - https://www.invidio.us/watch?v=-O5kNPlUV7w

As you can see, the layout is so minimalistic, that there is literally nothing to sift through in terms of porting. I really don't think it could be any easier site to port to NewPipe.

The main reason I bring this site up, is because if this site was added as an optional source for YouTube videos, then the user can effectively, disconnect from Google's YouTube entirely.

Start by reviewing the repository's existing source extractors and how optional sources are configured, then compare their entry points with the Invidious watch URL in the issue. Done means Invidious can be selected as an optional YouTube source and the example video yields the expected content and metadata without relying on Google's YouTube service.