jack: add option to disable monitor ports

Add a jack.show-monitor option (default true) that makes it possible
to hide the monitor ports.

Monitor ports are not enabled by default on JACK and maybe they also
should not for PipeWire. Or maybe we need some tweaks for some apps.

See #1760

src/daemon/jack.conf.in

@@ -60,6 +60,7 @@ context.modules = [
 jack.properties = {
      #node.latency       = 1024/48000
      #node.lock-quantum  = false
+     #jack.show-monitor  = true
      #jack.merge-monitor = false
      #jack.short-name    = false
      #jack.filter-name   = false