Give option to disable group mentions
Description
At GNOME's GitLab we have a group called GNOME where all developers are; and we also have a Twitter handle named @gnome... you can imagine where this is going :)
So the problem is that people keep mentioning @gnome in our issues for the twitter handler, and everyone at GNOME keep being notified when this happens. Unfortunately this happens often by accident, even after being informed to avoid it.
I can imagine this could happen with other GitLab instances that have a heavy use of groups (we have just 4) and also in case of people from outside wanting to grab attention (@all was disabled already for the this same issue).
Proposal
Allow group mentions to be disabled.
More granularity could be implemented too like a setting by group, but I guess to make a first viable product would be better to just have a system-wide setting.