event.response.emailSubject with the 6 digits code

### Is this feature request related to a new or existing Amplify category?

auth

### Is this related to another service?

Cognito

### Describe the feature you'd like to request

Hi,
Most of web apps give the log in code in the email subject too.
It is not a security risk because only the owner can read it.

Could you change and update it please ?

### Describe the solution you'd like

The 6 digits code in the email subject.

### Describe alternatives you've considered

None

### Additional context

_No response_

### Is this something that you'd be interested in working on?

- [ ] 👋 I may be able to implement this feature request

### Would this feature include a breaking change?

- [ ] ⚠️ This feature might incur a breaking change

The request concerns the Amplify CLI auth category and its Cognito email flow, but it names no source file, entry point, or test. Start by tracing how Cognito verification emails are configured and generated; done means the six-digit code appears in the email subject without breaking the existing authentication flow, with coverage for the resulting subject.

Written by the indexing model from the issue text.