create workgroup function for fairsharepoints admin group

Closes #974 (closed)

What does this MR do?

Creats a new workgroup function for fairsharepoints.

• If a workgroup with a fairsharepoint function is assigned only those admins are allowed to "freischalten" a fairsharepoint as well as edit them without being an responsible person of this fairsharepoint as long as it belongs to the district the workgroup is assigned to.

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

• quite

Links to related issues

Any relevant links (issues, documentation, slack discussions).

How to test

Steps a reviewer can take to verify that this MR does what it says it does e.g.

1. Checkout branch locally
2. Login as foodsaver
3. Create a new fairsharepoint
4. Check that only admins of the workgroup get the bell to "freischalten" a new fsp
5. Only admins of the workgroup can create a fairsharepoint without having it to be "freigeschaltet"

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
• use "state:" labels to track this MR's state until it was beta tested
• added an entry to CHANGELOG.md
• add 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 Beta Testing Repo:
  • 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.