Add an option to disable AGC (automatic gain control)

[arieshi255]

Is your feature request related to a problem? Please describe.
It's very annoying that there's no way to disable AGC. This is a default in Chromium, and it's up to each app to disable/add a toggle for it. Since Element relies on this SDK for calls, both projects need to add support for this.

Describe the solution you'd like
When calling getUserMedia(), you can specify an audio object with constraints. autoGainControl being set to false should resolve it, but ideally this will be a function parameter or something similar.

Describe alternatives you've considered
There is no alternative, considering this is a Chromium limitation.

Additional context
It's a trivial change, so please don't just shove this issue off. This is a feature a lot of people would appreciate. If there's any help needed to implement it, I'll see what I can do.

[DoM1niC]

Will fixed by #2434

[MrAnno]

Fixed by #2434.