Migration Guide from spray

TODO - will be written shortly.

• respondWithStatus also known as overrideStatusCode has not been forward ported to Akka HTTP, as it has been seen mostly as an anti-pattern. More information here: https://github.com/akka/akka/issues/18626
• respondWithMediaType was considered an anti-pattern in spray and is not ported to Akka HTTP. Instead users should rely on content type negotiation as Akka HTTP implements it. More information here: https://github.com/akka/akka/issues/18625