feat(playout): configure device for alsa and pulseaudio system outputs (#2654)

### Description

Add hardware configuration to liquidsoap so that users may
set hardware output in config.yml.

---------

Co-authored-by: jo <ljonas@riseup.net>

legacy/application/configs/conf.php

@@ -211,6 +211,7 @@ class Schema implements ConfigurationInterface
             /*    */->validate()->ifNotInArray(["alsa", "ao", "oss", "portaudio", "pulseaudio"])
             /*    */->thenInvalid('invalid stream.outputs.system.kind %s')
             /*  */->end()->end()
+            /*  */->scalarNode('device')->end()
             /**/->end()->end()->end()
 
             ->end()->end()