Support custom hostnames

[bbartels]

We have a situation where we are doing some routing based on the hostname with yarp.
So .service.com will route to a given provider. Ideally, we'd like to be able to test this functionality locally as well, however, you cannot use linux-dev-certs to trust hosts other than localhost.
Is this something that has been discussed before? Happy to submit a PR if the general idea is signed off!