Custom domains for resources, such as AppSync, Cognito

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

auth, api

### Is this related to another service?

_No response_

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

Usually I like to have the API and Authentication behind a custom domain, which is something is already feasible outside of Amplify. Why you may ask? Let's say that the production stack for some crazy reason is recreated causing a new hostname being generated, this would be a catastrophic thing as all apps that contains hardcoded information needs an update.

### Describe the solution you'd like

A domain/subdomain is pre-defined in Route53 that is then linked to AppSync and Cognito by the means of CloudFront (for AppSync) and standard configuration in Cognito.

### Describe alternatives you've considered

There are no alternatives really, unless I deploy a stack by hand which does this, but the configuration on Amplify client-side needs to support the new host names.

### Additional context

_No response_

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

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