Extend custom domain verification timeout to 7 or 14 days

**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, so 24 hours is far too short.

**Describe the solution you'd like**

Please change the timeout from 24 hours to at least 7 days, preferably 14 days.

Start by tracing how Amplify custom-domain verification is configured and where the 24-hour limit is enforced. Confirm whether the verification window can be changed to 7 or 14 days without affecting the DNS values or restart behavior; done means the longer timeout is implemented and verified for custom domains.

Written by the indexing model from the issue text.