Implement automation of translations

[larsrickert]

Why?

Follow up for #4141. We want to automate the translation for onyx so the languages are always complete when new translations are added in the future.

For this, a GitHub action should be added that can be triggered (or is triggered automatically) that adds missing translations for all available languages.

This is mostly already implemented on the branch larsrickert/4141-translations. We are currently blocked by an open feature request from AITxt.

Acceptance criteria

• a GitHub action is added that can be trigged manually for a branch that
  • translates all missing translations for all available languages using AITxt
  • creates a PR to the branch that it was triggered for with the updated translations
• tests are added that ensure that all languages are complete. You can use this test snippet: feat: support more languages #4855 (comment)
• the docs and showcase are updated to remove the "Translated keys" column on their i18n page

Implementation details

• larsrickert/4141-translations

DEV handover checklist

Storybook

DEV handover done with: @ADD_DEV_NAME_HERE

Testing

• covered by visual screenshot tests
• covered by functional tests (Playwright or unit test)

Other

• follow-up tickets were created if necessary (add links below)