k6: Import k6-0.48.0 as net/k6

k6 is a modern load-testing tool, built on our years of experience in
the performance and testing industries. It's built to be powerful,
extensible, and full-featured. The key design goal is to provide the
best developer experience.

Its core features are:

- Configurable load generation. Even lower-end machines can simulate
  lots of traffic.
- Tests as code. Reuse scripts, modularize logic, version control, and
  integrate tests with your CI.
- A full-featured API. The scripting API is packed with features that
  help you simulate real application traffic.
- An embedded JavaScript engine. The performance of Go, the scripting
  familiarity of JavaScript.
- Multiple Protocol support. HTTP, WebSockets, gRPC, and more.
- Large extension ecosystem. You can extend k6 to support your needs.
  And many people have already shared their extensions with the
  community!
- Flexible metrics storage and visualization. Summary statistics or
  granular metrics, exported to the service of your choice.

(leot)