Add OT collector trace exporter

[c24t]

Exporter to export traces to the OT collector: https://github.com/open-telemetry/opentelemetry-collector. Note that the release may be blocked on the release of https://github.com/open-telemetry/opentelemetry-proto.

See the js implementation: open-telemetry/opentelemetry-js#552.

[hectorhdzg]

open-telemetry/opentelemetry-proto#91

[Oberon00]

I did a prototype of a exporter for that protocol for Dynatrace-internal purposes already. It is not in shape for a proper PR, but if anyone wants to use it (for copy & paste or simply as a reference to look at), here is the code (I'd appreciate if you could use git commit --author if you based the code on this): https://gist.github.com/Oberon00/5c30bddfbb438129bcebee9190500bf1. It is not up to date with the latest changes though, off the top of my head, trace-id has changed from two int64s to a single byte array, span id from int64 to byte array and the agent package has been renamed to collector since.