🚀 [Feature] Simplify the mentioning for/of group members

[sushidave]

🚀 Feature

As a group member, I want to easily select members of my group in a group post or comment in order to mention/notify them.

Problem

Currently, I need to have the group overview page with the member list open in another browser tab to then mention them one by one in my group post or comment.

Solution

Possible solution: #7567