chore(servicecatalogappregistry): providing default values for Create…

…ApplicationTargetOptions (#22890)

----

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### Adding new Unconventional Dependencies:

* [ ] This PR adds new unconventional dependencies following the process described [here](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md/#adding-new-unconventional-dependencies)

### New Features

* [ ] Have you added the new feature to an [integration test](https://github.com/aws/aws-cdk/blob/main/INTEGRATION_TESTS.md)?
	* [x] Did you use `yarn integ` to deploy the infrastructure and generate the snapshot (i.e. `yarn integ` without `--dry-run`)?

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

packages/@aws-cdk/aws-servicecatalogappregistry/README.md

@@ -75,7 +75,10 @@ const app = new App();
 const associatedApp = new appreg.ApplicationAssociator(app, 'AssociatedApplication', {
   applications: [appreg.TargetApplication.createApplicationStack({
     applicationName: 'MyAssociatedApplication',
+    // 'Application containing stacks deployed via CDK.' is the default
+    applicationDescription: 'Associated Application description',
     stackName: 'MyAssociatedApplicationStack',
+    // AWS Account and Region that are implied by the current CLI configuration is the default
     env: { account: '123456789012', region: 'us-east-1' },
   })],
 });

packages/@aws-cdk/aws-servicecatalogappregistry/lib/target-application.ts

@@ -27,7 +27,7 @@ export interface CreateTargetApplicationOptions extends TargetApplicationCommonO
   /**
     * Application description.
     *
-    * @default - No description.
+    * @default - Application containing stacks deployed via CDK.
     */
   readonly applicationDescription?: string;
 }
@@ -90,10 +90,14 @@ class CreateTargetApplication extends TargetApplication {
   }
   public bind(scope: Construct): BindTargetApplicationResult {
     const stackId = this.applicationOptions.stackId ?? 'ApplicationAssociatorStack';
+    (this.applicationOptions.description as string) =
+            this.applicationOptions.description || `Stack that holds the ${this.applicationOptions.applicationName} application`;
+    (this.applicationOptions.env as cdk.Environment) =
+            this.applicationOptions.env || { account: process.env.CDK_DEFAULT_ACCOUNT, region: process.env.CDK_DEFAULT_REGION };
     const applicationStack = new cdk.Stack(scope, stackId, this.applicationOptions);
     const appRegApplication = new Application(applicationStack, 'DefaultCdkApplication', {
       applicationName: this.applicationOptions.applicationName,
-      description: this.applicationOptions.applicationDescription,
+      description: this.applicationOptions.applicationDescription || 'Application containing stacks deployed via CDK.',
     });
 
     return {