fix(dashboards): use correct scope for default DashboardFactory (#367)

Fixes #357

This was unintentionally changed during [this refactoring](6e04b20#diff-03751236dd3f86d2e1421165630d186616c9ca23c203b86ab195b36c5f1022f2) in between v3.0.4 and v3.0.5.

---

_By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license_

Author: Eugene Cheung

lib/facade/MonitoringFacade.ts

@@ -165,7 +165,7 @@ export class MonitoringFacade extends MonitoringScope {
     };
     this.dashboardFactory =
       props?.dashboardFactory ??
-      new DefaultDashboardFactory(scope, `${id}-Dashboards`, {
+      new DefaultDashboardFactory(this, `${id}-Dashboards`, {
         dashboardNamePrefix: id,
       });