Allow a custom domain verification period to be restarted after it times-out.

**Is your feature request related to a problem? Please describe.**

We offer our customers the option of using their own custom domain for our SaaS application, hosted on Amplify. When they choose a custom domain, we provide the two necessary DNS changes they must make -- one to add a CNAME for domain verification, and another CNAME for the custom domain.

The problem is that Amplify stops trying to verify after 24 hours, and the process cannot be restarted (with the same DNS values). Almost every large customer takes significantly longer than 24 hours to get their IT departments to make DNS changes.

There is currently a "work-around", which is not very useful. It's to delete the custom domain and then re-created it, which starts the 24-hour timeout counter again. The problem is that the Cloudfront domain which is the DNS target of the custom domain is changed at this point, so our customer must go back and try to update DNS, but again withing this 24-hour window.

**Describe the solution you'd like**

Add the ability to "restart" a custom-domain request. In this case, the existing Cloudfront domain will be reused, instead of deleting it and creating a new one.

BTW, this feature request is related to, but not the same as this one: https://github.com/aws-amplify/amplify-hosting/issues/2759

Start by tracing the custom-domain verification flow described in the issue, including the 24-hour timeout and the existing CloudFront target. Review related issue #2759 for context before determining where a restart could reuse the existing domain. Done means a timed-out verification can be restarted without changing the CloudFront DNS target.

Written by the indexing model from the issue text.