Add embedded video support.

[Spaghetto392]

Is your feature request related to a problem? Please describe.
There is a browser addon called 'Libredirect' that allows a user to automatically redirect to private frontends for various services. One of the features that Libredirect has is the ability to replace embedded YouTube videos with an equivelant embed for Invidious. Due to the lack of embedded support in Materialious, if a user sets a Materialious instance as their preferred redirect, all embedded videos will fail to load.

Describe the solution you'd like
Implement a embedded video mode that is accessed the same way as Youtube's.

Describe alternatives you've considered
Given that Libredirect does supply the option to disable redirects of embedded videos, a user could simply choose to turn that feature off.

Additional context
Libredirect doesn't technically have official support for Materialious, but a user can simply add it regardless as a "preferred instance." As long as the URL syntax is correct, Libredirect doesn't care.