Adding context propagation to net/http server instrumentation

[oxeye-gal]

Hi,

This PR attempts to add context propagation to the net/http server instrumentation.

We do it by iterating over the first bucket of the incoming request header map and trying to find the "traceparent" header.

This was tested with Go versions 1.12-1.19.

Our test environment consisted of instrumented Python application that sends a request to instrumented Go http server.

The produced trace looks like the following:

We would love to get your feedback on this.
Thanks!

[hnhbwlp]

I think it is necessary to check whether the traceparent exists before inserting elements into the map, because if the same key exists, there may be logic errors when writing the http header.

[vreynolds]

@oxeye-gal any interest in re-opening this in https://github.com/open-telemetry/opentelemetry-go-instrumentation ?

[oxeye-gal]

Hi @vreynolds, sure thing i'll do it later this week.

[MikeGoldsmith]

Hey @oxeye-gal - If you would like help porting this to the OTel repo, let me know -- I'm happy to help however I can.