Fix the legacy search index

What does this MR do?

Fixes the quick search index that is not working since the translation MR !2108 (merged)

I used to opportunity to refactor it a bit:

• the search results use a DTO
• they don't contain translatable texts anymore, which removes some legacy frontend code
• all utility functions in the backend are moved into the SearchTransaction class for consistency with the other modules

How confident are you it won't break things if deployed?

Very sure

Links to related issues

"Buddies werden nicht per Suchleiste angezeigt" in the beta group: https://foodsharing.de/?page=bezirk&bid=734&sub=forum&tid=154288&pid=882495#post-882495

How to test

1. Checkout branch locally
2. Login as foodsaver
3. Open http://localhost:18080/api/search/index and check that it contains JSON data
4. Search for something in the topbar and check that you can see buddies, stores, regions, and groups

Checklist

• added a test, or explain why one is not needed/possible...
• no unrelated changes
• asked someone for a code review
• set a "for:" label to indicate who will be affected by this change
• used "state:" labels to track this MR's state until it was beta tested
• added to the next milestone (see https://gitlab.com/foodsharing-dev/foodsharing/-/milestones, unless it has a "for:Dev" label)
• added an entry to CHANGELOG.md
• added a short text that can be used in the release notes
• Once your MR has been merged, you are responsible to create a testing issue in the Beta Testing forum: https://foodsharing.de/?page=bezirk&bid=734&sub=forum. Please change the MRs label to "state:Beta testing".
  • Consider writing a detailed description in German.
  • Describe in a few sentences, what should be tested from a user perspective.
  • Also mention different settings (e.g. different browsers, roles, ...) how this change can be tested.
  • Be aware, that also non technical people should understand.

Release notes text in German