[keycloak-dev] Ability to set hostname for server

Currently we have a few people having issues with the fact that we use the URL of the request as the hostname for Keycloak. For example to get the address sent in emails or as the iss value in tokens. This works fine as long as everyone accesses it using the proper domain name. However, it doesn't work when servers are on the same local network use the direct IP address or internal hostname. The simplest solution to this would be to add an option to set the hostname for the server. This would be configured in keycloak-server.json, but we'd also support setting it with a system property. Default would be to use the request-url as we do now, but once specified we would not use the request-url anymore and always use the configured hostname as the base URL.