Provide support for HTTP/2

[RustedBones]

As of today, Akka Http only allows using HTTP2 with bindAndHandleAsync method. Since .recordMetrics returns a flow, I can't use this library with HTTP2 which only takes HttpRequest ⇒ Future[HttpResponse] as handler.

[RustedBones]

async handler is now part of the API but connections metrics are not supported.

[bilal-fazlani]

The latest release of Akka HTTP has improvements for HTTP 2. Not sure if it helps

https://doc.akka.io/docs/akka-http/current/release-notes/10.1.x.html#akka-http2-support

[RustedBones]

Thanks for the notification @bilal-fazlani !

There are no significant changes on the API but I spotted this TODO comment on the Http2Ext that indicates a possible unification with Http API.

At this point the connections metrics could be added for Http2.

[RustedBones]

Small update on this.

Seems the unification goes the opposite way in akka-http 10.2. It favors the function handler instead of the stream, making it more difficult to access connections metrics

[RustedBones]

TelemetrySpi has been added to akka-http. akka-http-metrics should provide an implementation