[request] Add the mentioned user as watcher

[carlinux]

Hi, would be possible somehow to automatically add the mentioned user in the watcher list automagically?
We are using restricted permissions so only watchers can reply and see the conversation. Just mentioning someone triggers an email notification but it has no permissions to see the issue. Just the notification

[inhaledesign]

If this feature gets added, I vote that it be togglable in settings and not enabled by default. While I understand OP's use-case, I've found (having had this feature on other issue trackers) that often users get @mentioned just for a quick clarifying question. Auto-subscribing them to the issue ensures that they receive a bunch of e-mail notifications they don't need.