Workgroup function welcome

Closes #176 (closed)

What does this MR do?

Extends functionalities to workgroup admins to allow more flexibel subsidiarity decisions and user engagement.

In this case the bell-notification for new foodsavers can be extended to admins of a local workgroup and therefore is not dependend anymore on only ambassadors. If foodsaver want to be part of a welcome team now they can. It is not as big of a step to become ambassador.

When the workgroup is once created then the district can manage the admins themselves. At the moment it is only planned to have ONE welcome Group in a district.

If you want to have different welcome groups for certain part of the town then subdistricts would have to be created.

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

Quite

Links to related issues

#176 (closed)

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 Orgauser
3. Open "Bezirke Verwalten"
4. Create a workgroup under a region
5. Set an admin for this workgroup who is not an ambassador of this region
6. Set "Workgroup function" to "Begrüßung"
7. Save and logout
8. Login as a foodsaver
9. Join the district, under which the workgroup was created.
10. logout with foodsaver
11. Login with admin of the "Begrüßung" workgroup you set in setp 5.
12. Check the Bell - the user now should see the bell for newly joined user from step 8.

Screenshots (if applicable)

Settings in "Bezirke Verwalten" (only for orga). New Setting option "Arbeitsgruppenfunktion" with possible setting for "Begrüßung".

Additional to ambassadors of the district, admin of the workgroup for funktion with "Begrüßung" can see the bell of a new foodsaver who joined the district.

Admins of the welcome team are shown in the list of ppl in the district overview

The workgroup for welcome team is just a basic workgroup - as usual

Checklist

• added a test, or explain why one is not needed/possible...
• no unrelated changes
• asked someone for a code review
• joined #foodsharing-beta channel at https://slackin.yunity.org
• added an entry to CHANGELOG.md (description, merge request link, username(s))
• Once your MR has been merged, you are responsible to update the #foodsharing-beta Slack channel about what has been changed here. They will test your work in different browsers, roles or other settings
• EXECUTE DATABASE CHANGES BEFORE MERGING