Urls in settings require a port

Describe the bug

If you use the Urls setting and don't supply a port, when starting under ASP.Net Core you receive a timeout error.

The actual error is a NRE from this line: https://github.com/wiremock/WireMock.Net/blob/cbc28c235c711a47dad5d628b3172e159968159d/src/WireMock.Net.Minimal/Owin/AspNetCoreSelfHost.cs#L152

PortUtils.TryExtract has null annotations to say that the scheme out parameter will be null if TryExtract returns false, but there is a null-forgiving operator on the next line so you get a NRE.

Expected behavior:

Either no port is allowed and the code above should not run if TryExtract returns false; or the docs should be updated to explain that port is required on entries in Urls.

Test to reproduce

• 1 - Add a url to Urls without a port
• 2 - Start the server

Other related info

Side note: The exception thrown from Start is a timeout rather than the actual exception that occurred which made debugging the issue more difficult. It would be good to solve that as well.

BTW, I am happy to create a PR for this, but I'm raising the issue first for discussion.