Include zipkin server in the demo

[anyulled]

Hello, I recently presented a OpenTelemetry demo at my company, and one of the main benefits we saw of using OTel is being able to send tracing data to several exporters and compare these services.

I think it's a good idea to also include zipkin for receiving traces. Thus, anyone will be able to showcase both services without the hassle of configuring it.

If you like, I can create a pull request for it.