Add sleep and page.waitForTimeout doc to v0.52 & v0.53

[ankur22]

What?

Add sleep and page.waitForTimeout doc to v0.52 & v0.53. It's a new recommended best practice doc for the browser module.

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).

Related PR(s)/Issue(s)

Updates: #1719

[heitortsergent]

This is really awesome @ankur22, thanks for creating this! I made some small suggestions, mostly style related.

Another thing I wanted to point out, once this is ready to merge, we should apply the changes to the next folder as well so the docs stay in sync in future releases.

[ankur22]

Thanks for the review @heitortsergent! I've used all your suggestions in all versions of the doc, including in the next section.

[heitortsergent]

🚀

[inancgumus]

LGTM 👍