This deprecates span transports in favor of `spring-cloud-sleuth-zipkin2`
which:
* Supports RabbitMQ and Kafka automatically when adding spring-rabbit or spring-kafka deps
* Supports any io.zipkin.reporter2:zipkin-reporter sender, including Amazon X-Ray
* Defaults to zipkin v2 format, but can be configured to use zipkin v1 format as needed
This lowers the amount of maintenance on the project, as discussed in various issues
See #727
See #711
without this change there is no support for context propagation
with this change whenever you pass the `baggage-...` for http or `baggage_` for messaging headers then such a value will be propagated through your system
fixes#237
