Include obs-browser

Description:

While obs-browser is in a separate repository from the main source code of OBS Studio, the importance of browser sources to streaming - and the fact that this plugin is both an official OBS project and included in all official distribution methods of OBS Studio (Windows, MacOS, Ubuntu, and Flatpak) - indicates that our package in [extra] should include it as well.

Based on the obs-studio-browser AUR package, it shouldn't complicate packaging in any meaningful way.