container: expose priority and SCHED_OTHER policy

The more explicit API removes the arbitrary limit preventing use of SCHED_OTHER (referred to as SCHED_NORMAL in the kernel). This change also exposes priority value to set.

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

internal/outcome/shim.go

@@ -274,6 +274,7 @@ func shimEntrypoint(k syscallDispatcher) {
 	cancelContainer.Store(&stop)
 	sp := shimPrivate{k: k, id: state.id}
 	z := container.New(ctx, msg)
+	z.SetScheduler = state.Shim.SchedPolicy > 0
 	z.SchedPolicy = state.Shim.SchedPolicy
 	z.Params = *stateParams.params
 	z.Stdin, z.Stdout, z.Stderr = os.Stdin, os.Stdout, os.Stderr