[Feature Request] Add Checkbox to enable Pipewire audio upmixing

### Request
Add a checkbox to add upmixing by executing this command:
`sudo ln -s /usr/share/pipewire/pipewire.conf.avail/20-upmix.conf /etc/pipewire/pipewire-pulse.conf.d/ && systemctl --user restart pipewire pipewire-pulse wireplumber`
and, respectively:
`sudo rm /etc/pipewire/pipewire-pulse.conf.d/20-upmix.conf && systemctl --user restart pipewire pipewire-pulse wireplumber`

### Why?
By default [Pipewire has disabled upmixing since version 0.3.68](https://raw.githubusercontent.com/PipeWire/pipewire/0.3.68/NEWS). Therefore users with e.g. a 5.1 audio system will have music only be played back with the two front L/R speakers (even excluding the subwoofer) by default. Unless the 5.1 audio system itself detects the input being e.g. 2.0 and starts upmixing it to at least 2.1 itself the result will sound like a tin can. Unintentionally tested this myself with my PC connected to a Teufel Decoderstation 5 via analog cables.
Issue was also already encountered by users of other distros [[1](https://redlib.catsarch.com/r/ManjaroLinux/comments/12r6vgo/if_youre_using_pipewire_and_noticed_that_surround/), [2](https://forums.linuxmint.com/viewtopic.php?t=456403)].
Under Windows this automated upmixing seems to be the default and Pipewire indeed offers the settings so they can be easily enabled, which seems to be aimed at distro maintainers:

> - Upmixing was disabled again by default. We now ship config files that distros can install to enable upmixing again. (#3081)

However CachyOS doesn't enable it by default.

Given this might be a pretty important setting especially in the context of couch gaming I think a checkbox in CachyOS-Welcome could be the right place for this. :)

Start by locating the CachyOS-Welcome entry point for adding a settings checkbox and inspect how it handles privileged system commands. The request provides the enable and removal commands and the PipeWire restart sequence; done means the checkbox reliably applies or removes the configuration and restarts the listed user services.

Written by the indexing model from the issue text.