Add input sensitivity / microphone threshold feature

[crabdancing]

What problem are you trying to solve?

In Discord, and a number of other VOIP apps, there is a feature that allows the user to cap minimum volume at an arbitrary threshold. If dB are beneath this threshold, the mic switches off. This means that you can easily tune it so that background noise such as fans, typing, and breathing are ignored by your microphone.

What solution would you like to see?

To make Jitsi Meet more useful for larger business meetings, and to stay competitive with apps like Discord, it seems like a good idea to implement this feature.

Note that this feature request is a replacement for #14405, which met its tragic end at the hands of a stale bot.