Add icons to issue/merge request sidebar
We have icons for these attributes, and they are used throughout GitLab, such as in list views and issue boards. I think we should add these same icons to the sidebar, so that they reinforce the association with users because in the sidebar, they would be next to the actual words.
This is already the case with confidentiality and locking, because we have the icons to represent state. So it would be natural to include the rest in the sidebar.