Make the preferences test more robust

[obulat]

Fixes

Fixes #5001 by @obulat

Description

This PR updates the preferences test to make it less flaky:

• to find the switch, we use the getByRole Playwright locator with the checked property set to true or undefined. We add an extra expect, checking that the switch is enabled. This function is extracted to expectCheckboxState, which is added as a valid expect to the Openverse ESLint plugin.
• instead of testing the saved cookie value that is not visible by the users, we reload the page and check the switch state. If the state was saved in a cookie, then the state on page load should be updated.
• an extra check with the snapshot of all of the feature flag store state is added.

Testing Instructions

The Playwright e2e test should pass in the CI. I will re-run this step several times to make sure that the test is not flaky.

Checklist

• My pull request has a descriptive title (not a vague title likeUpdate index.md).
• My pull request targets the default branch of the repository (main) or a parent feature branch.
• My commit messages follow best practices.
• My code follows the established code style of the repository.
• I added or updated tests for the changes I made (if applicable).
• I added or updated documentation (if applicable).
• I tried running the project locally and verified that there are no visible errors.
• I ran the DAG documentation generator (ov just catalog/generate-docs for catalog
  PRs) or the media properties generator (ov just catalog/generate-docs media-props
  for the catalog or ov just api/generate-docs for the API) where applicable.

Developer Certificate of Origin

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[github-actions]

Latest k6 run output¹

$     ✗ status was 200
      ↳  99% — ✓ 7999 / ✗ 1

     checks.........................: 99.98% ✓ 7999      ✗ 1   
     data_received..................: 1.8 GB 9.0 MB/s
     data_sent......................: 1.0 MB 5.1 kB/s
     http_req_blocked...............: avg=14.34µs  min=1.84µs  med=3.36µs   max=6.96ms  p(90)=4.78µs   p(95)=5.15µs  
     http_req_connecting............: avg=10.54µs  min=0s      med=0s       max=6.91ms  p(90)=0s       p(95)=0s      
     http_req_duration..............: avg=531.19ms min=50.58ms med=475.54ms max=2.2s    p(90)=999.84ms p(95)=1.1s    
       { expected_response:true }...: avg=531.09ms min=50.58ms med=475.53ms max=2.2s    p(90)=999.83ms p(95)=1.1s    
   ✓ http_req_failed................: 0.01%  ✓ 1         ✗ 7999
     http_req_receiving.............: avg=139.07µs min=37.99µs med=102.33µs max=13.93ms p(90)=168.28µs p(95)=215.89µs
     http_req_sending...............: avg=19.94µs  min=6.1µs   med=17.45µs  max=2.53ms  p(90)=23.4µs   p(95)=28.75µs 
     http_req_tls_handshaking.......: avg=0s       min=0s      med=0s       max=0s      p(90)=0s       p(95)=0s      
     http_req_waiting...............: avg=531.03ms min=50.5ms  med=475.35ms max=2.2s    p(90)=999.72ms p(95)=1.1s    
     http_reqs......................: 8000   39.029563/s
     iteration_duration.............: avg=3.54s    min=1.1s    med=2.96s    max=10.48s  p(90)=7.84s    p(95)=8.3s    
     iterations.....................: 1200   5.854435/s
     vus............................: 3      min=3       max=30
     vus_max........................: 30     min=30      max=30

Footnotes

1. This comment will automatically update with new output each time k6 runs for this PR ↩