Build Notification to include custom domain link

### Before opening, please confirm:

- [x] I have checked to see if my question is addressed in the [FAQ](https://github.com/aws-amplify/amplify-hosting/blob/master/FAQ.md).
- [x] I have [searched for duplicate or closed issues](https://github.com/aws-amplify/amplify-hosting/issues?q=is%3Aissue+).
- [x] I have removed any sensitive information from my code snippets and submission.

### Amplify Hosting feature

Notifications

### Is your feature request related to a problem? Please describe:

Currently the build notification when enabled from Amplify console, do not include custom domain link. The only include the default amplify domain link

Current workaround: Using event bridge rule -> Lambda -> SNS -> email

### Describe how you'd like this feature to work

Build Notification to include custom domain link

Review the Amplify Hosting build notification flow and how custom domains are represented in notification payloads. Done means an enabled build notification includes the application's custom domain link instead of only the default Amplify domain; the issue names no files or tests to start from.

Written by the indexing model from the issue text.