hst: expose scheduling priority

This is useful when limits are configured to allow it.

Signed-off-by: Ophestra <cat@gensokyo.uk>

nixos.nix

@@ -140,6 +140,7 @@ in
                     inherit (dbusConfig) session_bus system_bus;
                     direct_wayland = app.insecureWayland;
                     sched_policy = app.schedPolicy;
+                    sched_priority = app.schedPriority;
 
                     container = {
                       inherit (app)