Support for propagating opentracing span context in metadata

[brunoribeiro]

Fahrschein already supports this, can we update the NakadiMetadata class to include the span ctx like in here

[ePaul]

Thanks for the suggestion.

I suppose what we actually want is to transport the span from when the event is passed to the library, not when it was passed to Nakadi (or maybe both?). Should we expose arguments for the span context map in the NakadiWriter interface, or get those implicitly by calling the OpenTracing implementation?

[ePaul]

I started a sketch of an implementation in #115.

[ePaul]

As mentioned in #115, a similar thing should be done with OpenTelemetry instead.