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

internal/queue/queue.go

@@ -27,6 +27,9 @@ type Config struct {
 }
 
 func NewQueue(config *Config) (_ *Queue, err error) {
+	if config.Client.Type() == "cockroach" {
+		return nil, nil
+	}
 	return &Queue{
 		driver: riverpgxv5.New(config.Client.Pool),
 		config: &river.Config{