Add missing playwright e2e docs to toc.json

[kevin940726]

What?

Fix missing playwright e2e docs.

Why?

See #45709 (comment)

How?

Add the links to toc.json.

Testing Instructions

Not sure how to test?

[github-actions]

Flaky tests detected in 4522ff1.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/4270555236
📝 Reported issues:

• [Flaky Test] should navigate block hierarchy using only the keyboard #47640 in specs/editor/various/block-hierarchy-navigation.test.js

[Mamaduka]

Renamed the migration.md file. That should fix the failing CI check.

[Mamaduka]

I couldn't find any details on testing documentation changes like these. So let's merge changes and test on the site.