Indicate users that are a sole owner of a group in `Admin` -> `Users` -> `Groups and projects`

Proposal

Follow-up to #337556 (comment 757594536)

Indicate the groups that the user is a sole owner of.

Implementation plan

1. In app/views/admin/users/projects.html.haml#L11 use the solo owned groups method to check if the user is the sole owner of the group. If they are use gl_badge_tag to render a badge.
2. Investigate any potential N+1 issues