Update docs structure, rename Configure k6 Intellisense page

[heitortsergent]

What?

• Move "Set up" section above "Get started"
• Rename "Configure k6 Intellisense" page to "Configure your code editor"
• Add "Next steps" section to "Configure your code editor" page

Before

After

Checklist

• I have used a meaningful title for the PR.
• I have described the changes I've made in the "What?" section above.
• I have performed a self-review of my changes.
• I have run the npm start command locally and verified that the changes look good.

• I have made my changes in the docs/sources/next folder of the documentation.
• I have reflected my changes in the docs/sources/v{most_recent_release} folder of the documentation.
• I have reflected my changes in the relevant folders of the two previous k6 versions of the documentation (if still applicable to previous versions).

[heitortsergent]

@oleiade this PR includes some of the changes we talked about. 🙇