fix(facade): avoid duplicated construct names for default dashboard factories (#154)

If you have multiple facades in the same app using the default `dashboardFactory`, you'll end up with errors like:

```
[...]/node_modules/constructs/lib/construct.js:335
            throw new Error(`There is already a Construct with name '${childName}' in ${typeName}${name.length > 0 ? ' [' + name + ']' : ''}`);
            ^

Error: There is already a Construct with name 'Dashboards' in MyMonitoringFacade [MyApp-NestedTest]
[...]
```

---

_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.d.ts.map

@@ -116,11 +116,13 @@ export interface MonitoringFacadeProps {
    * @default empty (no preferences)
    */
   readonly metricFactoryDefaults?: MetricFactoryDefaults;
+
   /**
    * Defaults for alarm factory.
    * @default actions enabled, facade logical ID used as default alarm name prefix
    */
   readonly alarmFactoryDefaults?: AlarmFactoryDefaults;
+
   /**
    * Defaults for dashboard factory.
    * @default `DefaultDashboardFactory`; facade logical ID used as default name
@@ -170,7 +172,7 @@ export class MonitoringFacade extends MonitoringScope {
     scope: Construct,
     defaultName: string
   ): IDashboardFactory {
-    return new DefaultDashboardFactory(scope, "Dashboards", {
+    return new DefaultDashboardFactory(scope, `${defaultName}-Dashboards`, {
       dashboardNamePrefix: defaultName,
     });
   }

lib/facade/MonitoringFacade.ts

@@ -3,15 +3,31 @@ import { Template } from "aws-cdk-lib/assertions";
 import { MonitoringFacade } from "../../lib";
 
 describe("test of defaults", () => {
-  const stack = new Stack();
-  new MonitoringFacade(stack, "Test");
-  const result = Template.fromStack(stack);
-
   test("only default dashboard gets created by default", () => {
+    const stack = new Stack();
+    new MonitoringFacade(stack, "Test");
+    const result = Template.fromStack(stack);
+
     result.resourceCountIs("AWS::CloudWatch::Dashboard", 1);
 
     result.hasResourceProperties("AWS::CloudWatch::Dashboard", {
       DashboardName: "Test",
     });
   });
+
+  test("handles multiple facades", () => {
+    const stack = new Stack();
+    new MonitoringFacade(stack, "Test1");
+    new MonitoringFacade(stack, "Test2");
+    const result = Template.fromStack(stack);
+
+    result.resourceCountIs("AWS::CloudWatch::Dashboard", 2);
+
+    result.hasResourceProperties("AWS::CloudWatch::Dashboard", {
+      DashboardName: "Test1",
+    });
+    result.hasResourceProperties("AWS::CloudWatch::Dashboard", {
+      DashboardName: "Test2",
+    });
+  });
 });