Provide Hystrix event stream to visualize circuit breaking

[Hystrix Dashboard](https://github.com/Netflix/Hystrix/wiki/Dashboard) can help visualize the health of the Envoy mesh based on information provided.
The specification format is discussed [here](https://github.com/Netflix/Hystrix/wiki/Metrics-and-Monitoring) and [here](https://github.com/Netflix/Hystrix/tree/master/hystrix-contrib/hystrix-metrics-event-stream).