Misc scenario edits

[MattDodsonEnglish]

This PR could be rebased. For context, read the commit messages. Each commit is atomic and closes a minor open issue about scenarios.

There's still a good deal of work to do about helping users choose executors, but at least a k6 doc will now appear when someone searches "k6 coordinated omission".

I'm not crazy about the title "Advanced examples," either―what makes them so advanced?―but that can be fixed in a different commit.

[github-actions]

There's a version of the docs published here:

https://mdr-ci.staging.k6.io/docs/refs/pull/936/merge

It will be deleted automatically in 30 days.

[na--]

I don't understand what you mean here, sorry 😕 You can't have different setup() or teardown() per scenario (see grafana/k6#1638, though it will probably be solved by actually implementing grafana/k6#1342)

[MattDodsonEnglish]

I see now it's not specific enough. Thanks for pointing it out. What about this?

 Export multiple scenarios as functions in [VU code](/using-k6/test-lifecycle)

About the strange terminology: a month ago we defined lifecycle function as

a function called in a specific sequence in the k6 runtime.

We changed "callbacks" to "lifecycle functions" because callback sounded like a JS callback. It wasn't so obvious that it was to the Go runtime. Discussion here: #845.

[MattDodsonEnglish]

I'm trying to communicate what is done in this example, by the way.
Different scenarios run different VU logic.

export function contacts() {
  http.get('https://test.k6.io/contacts.php', {
    tags: { my_custom_tag: 'contacts' },
  });
}

export function news() {
  http.get('https://test.k6.io/news.php', { tags: { my_custom_tag: 'news' } });
}

[na--]

LGTM except the minor inline suggestions and questions I left

[na--]

LGTM except the broken list

[MattDodsonEnglish]

Thank you for the detailed review, as always!