I want to be able to filter issues on confidentiality status

Description

There are projects with confidential issues, including this gitlab-ce project. I want to be able to filter the issue on confidentiality status. E.g. great that there are lots of security related issues out there, but the confidential ones are probably the more interesting ones I want to pay attention to. I have no way of picking those out now.

Proposal

Add filter option for those users that have access to confidential issues, to filter on confidentiality status.