Add Hold-to-Deafen and Hold-to-Attenuate Keybind Actions

At present there is only Toggle Deafen available. While usable, it's less convenient for quickly stifling someone who regularly forgets to mute themselves; most especially when co-livestreaming with someone speaking to their own chat.

The ability to briefly hold-deafen would go a long way to mitigate that.

Additionally, while Priority Speaker is absolutely a thing, it's less-useful in a co-streaming scenario. A keybind to hold-attenuate incoming voice audio would be very handy, maybe with a slider to set just how much to drop it. That would allow you to be heard clearly (on your own stream), while at the same time being able to keep an ear on the background conversation and not hard-drop in and out.

A smooth ramp up and down on deafen/return (or attenuate) would also be appreciated, for added polish.