[SRU] buffer size and sample rate no longer updates

[Impact]

ubuntustudio-installer now contains a separate application for configuring the audio subsystem, which may in the future be spun-off into its own binary package. Initially, it was meant to simply switch systems between the PipeWire and the legacy PulseAudio/JACK configuration (an installer function). However, it became clear that it needed to be able to configure the PipeWire configuration as well.

This used to be as simple as changing the PIPEWIRE_QUANTUM environment variable with a logout/in, but this changed with the version of PipeWire in Mantic and required a somewhat higher level of complexity involving the `pw-metadata` command. This was not foreseen before release.

This also requires a systemd user service that applies these settings at login, also part of this change.

[Test Case]

With Ubuntu Studio installed:

 * Open Patchance
 * Note the sample rate and buffer (1024/48000 is the default)
 * Go to Ubuntu Studio Audio Configuration
 * Change the sample rate and buffer to something like 512 96000
 * Log out and in
 * Open Patchance
 * Note the sample rate and buffer *HAS NOT CHANGED* <- This is the problem
   ** Expected result is that it did change

[What could go wrong]

The only regression here is that in order to change the buffer size and sample rate, people will have to go back to the Audio Configuration utility to do so as opposed to whatever interface they are in, but the plus side is that it will no longer require a relog.