Add support for vert.x 4 event bus

[JSchering]

Please add support for tracing calls to the vert.x 4 event bus. Without this integration Traces through a microservice application built using vert.x will not show all the different services called but only the web service or api front end. The vert.x event bus is a core feature of vert.x and should be part of any implementation to trace through a vert.x application.

[swcm-mnestler]

We would also be interested in added EventBus support. Vert.x already provides some EventBus integration with other tracing libraries, maybe they can be of inspiration https://github.com/eclipse-vertx/vertx-tracing