Add information on how to format and lint k6 scripts

[na--]

Prompted by https://community.k6.io/t/linting-k6-scripts/1277

[ppcano]

https://k6.io/blog/how-to-lint-k6-tests-and-add-a-pre-commit-hook/ touches more extensively this topic.

Perhaps, instead of a dedicated section, we could cover this as part of a more general tutorial for recommendations to set up your k6 project.

[matthewbordas]

Any updates? On top of documentation, it would be nice if k6 provided a eslint extension that we could use to extend our .eslintrc files.

[ppcano]

@matthewbordas, this project has a .eslintrc file used to validate the documentation examples.

[na--]

Another related issue: grafana/k6#2992