[Feature Request]: Add a shortcut to increase and decrease volume level

[ghost]

Description

Hello devs. I would like to share the idea of adding the possibility to have a shortcut to increase and decrease the volume of PCSX2.

Reason

With this addition it will be possible to increase and decrease the volume without having to minimize or pause the emulation.

Examples

As Dolphin and other projects. Volume 0-100.

[lightningterror]

Dupe of #6427