Akka-http server metrics instrumentation broken for HTTP2 since akka-http 10.5.1

[adisnep]

Version 10.5.1 of akka-http comes with a refactoring for the handleWithStreamIdHeader method of the akka.http.impl.engine.http2.Http2Blueprint which brakes the server metrics instrumentation because this method is used by Kamon with reflection to pass info required to collect these metrics (for specific details regarding the refactoring check the following commit akka/akka-http@02bb987). Due to the current method signature the info necessary to collect the metrics can't be carried using the handleWithStreamIdHeader method anymore so we need a different way of carrying and extracting it.

My proposal will be to use the advise method instead of the intercept method in Kamon to hook on the same method handleWithStreamIdHeader ofakka.http.impl.engine.http2.Http2Blueprint and extract the necessary info simply because this is agnostic of the method signature(I see it more future proof than the current approach) and also used in other places in Kamon.

[adisnep]

I opened the following PR #1374 to address the issue. Please let me know you thoughts about it.