Add tuna plugin

[ghost]

Show information what music you're listening to on stream, this will be very useful for streamer who want to show what song or even video they are listening too.

https://github.com/univrsal/tuna
https://git.vrsal.xyz/alex/tuna

[GeorgesStavracas]

The ideal case would be the plugin to be made available on Flathub by the author. If you think this plugin is valuable, I encourage letting the author know about Flathub! In the meantime, you can compile and install manually as described here: https://github.com/flathub/com.obsproject.Studio/wiki/Plugins#method-2-config-folder