Current Situation

The frontend testing documentation is currently split between two pages, in two separate sections:

https://docs.openverse.org/frontend/guides/test.html
https://docs.openverse.org/frontend/reference/playwright_tests.html

The latter is linked by the playwright bot comment, but only the former includes instructions for actually updating the playwright test snapshots.

Suggested Improvement

We should combine these documents into a single frontend testing documentation page. Snapshots are now used on both playwright and jest tests, so it's important that these instructions are visible and easy to find for all cases of frontend testing. The division of the two is confusing anyway.

1. Move the testing guide into a single testing reference page
2. Update the playwright bot comment to link to the right section of the new page
3. Add redirects in the documentation configuration so old links continue to work

Benefit

Prevent confusion like #4499 (comment)

Additional context

Make sure to add redirects.