[bug#66877] [WIP PATCH 1/1] gnu: home: services: Add home-pipewire.

[chris]

Hello, I would like to share my experience that using pipewire without dbus on 
guix is practical: and so, it would be great if the home-pipewire-service could 
be used without dbus. Having said that, only a minority of people use dbus-free 
systems so feel free to ignore me and I do not want to block this patch.

In case it is useful, here is pipewire is used sans dbus. Guix home is 
configured to write the pipewire and three wireplumber config files, as 
described at this link https://wiki.alpinelinux.org/wiki/PipeWire#Configuration 

.config/pipewire/pipewire.conf
.config/wireplumber/wireplumber.conf
.config/wireplumber/main.lua.d/80-disable-dbus.lua
.config/wireplumber/bluetooth.lua.d/80-disable-logind.lua

When pipewire and wireplumber are installed with those files in place, start 
pipewire and wireplumber sequentially to get working sound. I use this in my 
.config/sway/config (possibly this is copy-pasted from unmatched-paren)
```
exec_always killall -wqr "(pipewire|wireplumber)" \
  || sleep 1 && ((pipewire &); sleep 2 && (wireplumber &))
```