Add "user-others" icon

Summary:
BUG: 407782

Needed to represent permissions for other users.

Test Plan: Search for user-others in Cuttlefish.

Reviewers: VDG, ndavis, ngraham

Reviewed By: VDG, ngraham

Subscribers: ngraham, kde-frameworks-devel, VDG

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D22822