Feature request: add command to adjust volume of all applications except for NVDA

[mltony]

I propose to add command that would adjust volume of all running applications except for NVDA. As usual, I will implement this myself if approved.

Description

This feature is really an integral part of #16051. The rationale is when we are splitting all sounds into NVDA channel and all other apps channel, there must be a way to control the volume of both channels separately. As for UI, I see there are two options:

1. To be consistent with NVDA volume, we can add a new setting in synth settings ring. The drawback of this is that it's not logical since this setting has nothing to do with synth settings.
2. Alternatively, we can create a separate command for that, say NVDA+Alt+PageUp/PageDown.

Prior discussion

#16037

Technical details

Technical detail 1 from #16051 applies here as well as we need to call the same wasapi COM interface.