Add ability to @mention anyone on GitLab, even if they're not part of a group or project
Description
I run a GitLab instance of about 25 users for my company. I would like to be able to @mention anyone who has a GitLab account on my server - not just those who are part of a project, group, or are already participating in the discussion.
Background
Most of my accounts are users and not developers, and thus don't use GitLab. I'd like to change that. To better engage them and to get them to actually use this tool, I'd like to @mention them so that they get the email notification and can view (if not participate in) the discussion that's going on.
Obviously for giant sites such as gitlab.com, this should be disabled. Not only would it promote spam, but it would make the @mention dropdown list take far too long to load.
Proposal
Add an admin page option or gitlab.rb parameter that enables instance-wide @mentions.
~"feature proposal"