Unify, format, and run tests against examples

[olegbespalov]

What?

• Format examples according the k6-docs standard (https://github.com/grafana/k6-docs/blob/main/.eslintrc)
• It also runs the test against these examples

Note that: import/export examples are commented on since they are actually catch a data race that should be resolved after #76

Sorry for the big PR. It's better to check by commit; the first commit could be skipped since it's auto-formating.

Why?

Unifying examples should improve the documentation and simplify their maintenance.

A pull-request starter #67 (comment)

Running the tests against examples should help with finding degradations like #68

[olegbespalov]

@mstoykov FYI, after including import/export (data race has gone with #76 ), I've found that one of the examples become broken (:tada:) and I include a minor fix 445ad03 to this PR. Hope that works!

[olegbespalov]

@joanlopez Since this PR is mostly about auto-applying the eslint + moving things around, I'm going to merge it as it is (since I need a couple more based on it). If you have any other feedback, feel free to bring it, and I'll iterate on it separately with PRs if needed.