Looks like trace mdc logging is not supported

Besides traces are sampled and sent to collector, we wanna traces to be added to mdc, so that whenever there is a log line for a request the corresponding traceId would be present.
I know that zipkin brave supports it from here https://github.com/apache/incubator-zipkin-brave/tree/master/context/slf4j. ---- Looks like ruby doesn't ? 