Make Rideshare examples use k6

As a continuation of the work to integrate Pyroscope and k6, we need to modify Rideshare to

- Have a k6 load test script
- Use the experimental Pyroscope Go SDK API that integrates with k6 (https://github.com/grafana/pyroscope-go/pull/99)

Since the Rideshare example doesn't expose itself to the public internet, we need a way to execute load tests from within a Kubernetes cluster. It seems like we can use the [k6 k8s operator](https://github.com/grafana/k6-operator) to accomplish this.