(aws-apigateway): Where does domainNameAliasTarget come from for imports?

### link to reference doc page

https://docs.aws.amazon.com/Route53/latest/APIReference/API_AliasTarget.html

### Describe your issue?

### Similar Issues
https://github.com/aws/aws-cdk/issues/6804
https://github.com/aws/aws-cdk/issues/4887

### Question
When doing an import how are you supposed to derive `domainNameAliasTarget`? Can an example be given for how this is sourced?

### Explanation
`domainNameAliasHostedZoneId` is a private value for both Regional and Edge endpoints. Meaning, Zone `Z1UJRXOUMOOFQ8` does not belong to any of my accounts and is called out the [docs](https://docs.aws.amazon.com/general/latest/gr/apigateway.html) as a hard-coded value. The responses in those other two issues are assuming you're creating a new APIGW Domain and not importing one. My use-case requires importing rather than creating a new domain. The referenced doc page doesn't even address the field at all even though it does others. Executing `aws apigateway get-domain-name` does not reveal what the alias target is. Trying to query the Route 53 service with the `Z1UJRXOUMOOFQ8` zone ID naturally results in an `AccessDenied` error.

Start with the Route53 AliasTarget reference and the API Gateway documentation linked in the issue, then compare the related discussions in issues 6804 and 4887. Check what aws apigateway get-domain-name exposes for imported domains and document how domainNameAliasTarget and domainNameAliasHostedZoneId are sourced. Done means an example explains the import case without requiring access to the hosted zone.

Written by the indexing model from the issue text.