feat: implement doctrine-based fulltext search

[benjaminfrueh]

📝 Summary

Replaces TNTSearch with nextcloud database full-text search using doctrine.

🏁 Checklist

• [x] Code is properly formatted (npm run lint / npm run stylelint / composer run cs:check)
• [x] Sign-off message is added to all commits
• [ ] Tests (unit, integration and/or end-to-end) passing and the changes are covered with tests
• [ ] Documentation (README or documentation) has been updated or is not required