Extract unit interface from session

Closes #1951 (closed)

What does this MR do?

This MR use the interface/branch of !3354 (merged).

The CurrentUserUnitsInterface is implemented by the Session-class itself. This MR extracts the implementation into an independent class. This allows to remove the code from Session class in future and is the first implementation of the unit check function from session with integration tests, so that later an implementation for Redis could be realized.

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

I hope not, not all modules are well tested.

Links to related issues

How to test

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
• set the "API change" label if changes in the API are not backward compatible
• 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.