Resolve "create REST Api Endpoint for /statistik"

Closes #1770 (closed)

What does this MR do?

• implements the end point for the /api/statistics route
• implements Unit and Functional Test
• refactor Annotations to Attributes
• changes the sort order of the overall statistics from collection quantity to number of collections
• adds three statistics times (total/within 3 months/current month)

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

sure

Links to related issues

How to test

Use the Api Doc

Screenshots (if applicable)

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
• 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 in the release notes to /release-notes/YYYY-MM.md
• Once your MR has been merged, you are responsible to create a testing issue in the Beta Testing forum: https://foodsharing.de/region?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.

Closes #1770 (closed)