Use new onboarding (merge main and onboarding)

[TimoPtr]

Summary

WIP

Checklist

• [ ] New or updated tests have been added to cover the changes following the testing guidelines.
• [ ] The code follows the project's code style and best_practices.
• [ ] The changes have been thoroughly tested, and edge cases have been considered.
• [ ] Changes are backward compatible whenever feasible. Any breaking changes are documented in the changelog for users and/or in the code for developers depending on the relevance.

Screenshots

Link to pull request in documentation repositories

User Documentation: home-assistant/companion.home-assistant#

Developer Documentation: home-assistant/developers.home-assistant#

Any other notes