(aws-amplify): Allow adding notification to amplify app

### Describe the feature

I couldn't find any APIs in CDK which allows us to add email notification to our amplify app.
Reference - https://docs.aws.amazon.com/amplify/latest/userguide/notifications.html

### Use Case

I want to add emails for getting notification via CDK only instead of doing it via AWS console

### Proposed Solution

Add a method like `addBranch` -> `addEmailNotification` there we can pass an array

### Other Information

_No response_

### Acknowledgements

- [ ] I may be able to implement this feature request
- [ ] This feature might incur a breaking change

### CDK version used

2.19.0 (build e0d3e62)

### Environment details (OS name and version, etc.)

Manjaro Linux x86_64

Locate the Amplify CDK construct and its existing addBranch API, then read the AWS Amplify notifications documentation linked in the issue. The work is done when email notifications can be configured through CDK with the proposed array-based API and the corresponding construct behavior is covered by tests.

Written by the indexing model from the issue text.