Replace PlayWright links with k6 Browser ones

[andrewslotin]

What?

Replaced references to PW docs with corresponding links to k6 docs.

Checklist

• [x] I have used a meaningful title for the PR.
• [x] I have described the changes I've made in the "What?" section above.
• [x] I have performed a self-review of my changes.
• [x] I have run the npm start command locally and verified that the changes look good.
• [x] I have made my changes in the docs/sources/next folder of the documentation.
• [x] I have reflected my changes in the docs/sources/v{most_recent_release} folder of the documentation.