Related to #1860.

From feedback with folks on the team, the k6 OSS docs don't have a clear section focused on how to write tests. We explain all the options available for how to use k6, but we are missing a clear "How to write tests" section. This is something that we have in the Grafana Cloud k6 docs, under "Author and run tests".

We do have a "Test authoring" section two levels deep in the current IA. We've just added a new page to it documenting the k6 new command, but this seems like a good time to update that section and bring it up in the current hierarchy.

We could:

• Move the "Test authoring section" to the root level, above "Using k6".
• Rename the section to "Author and run tests" to match the Grafana Cloud k6 docs.
• Add content to the index page for the section.
• Review the existing pages in that section (Test builder, Create tests from a recording)