!htc #15726: Akka HTTP with the new DSL

/cc @jrudolph @sirthias 

TODO:
 - [X] Port http-core
 - [x] Port rest of http
 - [ ] Port to the new IO abstraction
 - [x] get rid of unnecessary materializer parameters
these durations should probably be `.dilated` and I think they are unnecessary small (build servers are sometimes very slow)