fix: allow port in endpoint for aws private link validation

[MadJlzz]

Creating a new client for an endpoint url in the form hostname:port makes IsAmazonPrivateLinkEndpoint return false since the regex used to verify if that url is a valid aws private link does not match when it contains a port.

I propose to perform the validation on Hostname() instead of Host to always validate agains the actual hostname.

I've added some tests to prove that it works