Replace Bootstrap utility classes with GitLab UI utility classes in `app/views/users/show.html.haml`

Summary

Follow-up to !66493 (comment 637200196) we should replace all of the Bootstrap utility classes in app/views/users/show.html.haml with GitLab UI utility classes.

Improvements

Move closer towards a Bootstrap utility class free GitLab.

Risks

Slight visual regressions. Should be fairly easy to mitigate by comparing before and after screenshots

Involved components

• app/views/users/show.html.haml