[dev-overlay] add a11y test (#75523)
Added a11y test, but haven't enabled for the CI. Will follow up to
resolve the test result.
You can manually test a11y at the storybook portal:
https://github.com/user-attachments/assets/72929e65-bd70-481e-ac2f-1b518c344373
Closes https://linear.app/vercel/issue/NDX-584/add-a11y-tests
