fix(apprunner): the Service class does not implement IService (#32771)

### Issue # (if applicable)

Closes #32745 

### Reason for this change
`Service` should implement `IService`.
However at the moment, it doesn't.

### Description of changes
Modified `Service` class to implement `IService`.

### Describe any new or updated permissions being added
None


### Description of how you validated changes
No validation was needed as only interface implementation was added.

### Checklist
- [x] My code adheres to the [CONTRIBUTING GUIDE](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md)

----

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

Author: mazyu36

packages/@aws-cdk/aws-apprunner-alpha/lib/service.ts

@@ -1103,6 +1103,7 @@ export interface IService extends cdk.IResource {
 
   /**
    * The ARN of the service.
+   * @attribute
    */
   readonly serviceArn: string;
 }
@@ -1178,7 +1179,7 @@ export abstract class Secret {
 /**
  * The App Runner Service.
  */
-export class Service extends cdk.Resource implements iam.IGrantable {
+export class Service extends cdk.Resource implements IService, iam.IGrantable {
   /**
    * Import from service name.
    */