Allow @mention notification when the user is not part of the Security level

Issue Summary

Ability to restrict @mention users only from the specific Issue security level when the Issue security is applied

Actual Results

When a user is not part of the issue security and the user is @mentioned in a ticket, they will not be getting any notification. This is working as expected for security reasons. 

Expected Results

But there could be scenarios where the @mentioned user should only get the notification of the comment added and not have access to the ticket.

So the customer requirement is to enable/disable @mention for certain issue security levels.

Or

When the user in the Issue security @mentions the user the Notification should trigger.