pipewire.conf.in: use absolute path to pipewire-media-session

So pipewire daemon is able to find pipewire-media-session from the
location it's installed to, even when it's not in $PATH.

For the `pw-ininstalled.sh` and `make run` invocations, provide a
`src/daemon/pipewire-uninstalled.conf` that still uses the relative
path, but isn't installed.
2 jobs for pipewire-media-session-absolue-path in 1 minute and 1 second (queued for 1 second)