Welcome Bells only for Admins of welcome Group
Description
According of the result of beta-testing and an survey in the ambassador forum the welcome bell should only be shown to admins of the welcome group.
Goal
Evidence
https://gitlab.com/foodsharing-dev/foodsharing-beta-testing/-/issues/12#note_371277759
Solution
Instead of merging the arrays of bot and welcome admins only use welcome admins for new bells if there are any.