Zipkin storage implementation to forward spans to another Zipkin server (collector).
Before:
[ instrumented client ] --> ( transport ) --> [ zipkin server ]
Now:
[ instrumented client ] --> ( transport 1 ) --> [ zipkin forwarder ] --> ( transport 2 ) --> [ zipkin server ]
Where transport 1
could be HTTP or gRPC, and transport 2
could be Kafka or RabbitMQ.