Graduate `k6/experimental/websockets` as stable module

[olegbespalov]

What?

In the https://github.com/grafana/k6/releases/tag/v0.40.0 we introduced the new experimental module k6/experimental/websockets that implements WebSocket API.

This issue is for tracking the path of the extension; here, we could give some updates on its status.

Why?

The long-term plan is to replace the existing k6/ws with this new extension once we prove that it satisfies the customers' needs and is stable enough.

• [x] https://github.com/grafana/xk6-websockets/issues/35
• [ ] https://github.com/grafana/k6/issues/4770