helper/proc: expose setup file

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

internal/app/init/main.go

@@ -41,7 +41,7 @@ func Main() {
 		payload    Payload
 		closeSetup func() error
 	)
-	if f, err := proc.Receive(Env, &payload); err != nil {
+	if f, err := proc.Receive(Env, &payload, nil); err != nil {
 		if errors.Is(err, proc.ErrInvalid) {
 			log.Fatal("invalid config descriptor")
 		}