fix(cmd): clarify notification config handling (#9459)

# Which Problems Are Solved

If configuration `notifications.LegacyEnabled` is set to false when
using cockroachdb as a database Zitadel start does not work and prints
the following error: `level=fatal msg="unable to start zitadel"
caller="github.com/zitadel/zitadel/cmd/start/start_from_init.go:44"
error="can't scan into dest[0]: cannot scan NULL into *string"`

# How the Problems Are Solved

The combination of the setting and cockraochdb are checked and a better
error is provided to the user.

# Additional Context

- introduced with https://github.com/zitadel/zitadel/pull/9321

cmd/setup/setup.go

@@ -467,10 +467,14 @@ func startCommandsQueries(
 		config.DefaultInstance.SecretGenerators,
 	)
 	logging.OnError(err).Fatal("unable to start commands")
+
+	if !config.Notifications.LegacyEnabled && dbClient.Type() == "cockroach" {
+		logging.Fatal("notifications must be set to LegacyEnabled=true when using CockroachDB")
+	}
 	q, err := queue.NewQueue(&queue.Config{
 		Client: dbClient,
 	})
-	logging.OnError(err).Fatal("unable to start queue")
+	logging.OnError(err).Fatal("unable to init queue")
 
 	notify_handler.Register(
 		ctx,