Show custom attributes of user objects in admin view

Problem to solve

Currently Gitlab's API allows to set and retrieve custom attributes via Custom Attributes API (https://docs.gitlab.com/ce/api/custom_attributes.html).

It would be handy to see those attributes in the user details page which is only accessible to the administrator (https://git.yourhost.tld/admin/users/sszott).

Further details

(Include use cases, benefits, and/or goals)

Proposal

List all custom attributes on the user details page, e.g. https://git.yourhost.tld/admin/users/sszott

What does success look like, and how can we measure that?

The user details page list all custom attributes.

/label ~"feature proposal"