Add Keybind for attenuation toggle

It's a very handy feature, but I would rarely use it, me and a friend use screenshare to watch youtube videos together or listen to music (cause spotify integration isn't great yet) so it's great that the music for example gets decreased in volume when he talks, however, if he sings for example, or makes a small noise it gets turned down aswell, making for a choppy experience.

This is easily fixed if I could toggle/hold a button when I hear he is speaking so I can actually understand him and than toggle it off again/release the button when he is done.