Add logRequestResponse to Akka HTTP

[hkeeler]

It would be very useful to have access logs at the Akka HTTP level, similar to what we have for Nginx and Gunicorn now. I think Akka HTTP supports this via DebuggingDirectives. The usage is more complete under logRequest, though I think logRequestResponse is even better since, unlike a simple access log, you get the full response as well...which is very useful when dealing with RESTful APIs.

I've added this as M3, but it is not a high priority.