Username wrapping on small viewports

What does this MR do?

The MR provides a way to render username information on MRs on the small screens. The solution is based on progressive enhancement and hence default CSS properties are for the smallest screens that get enhanced for large screens using media queries. The visual solution is based on the proposed mockup in https://gitlab.com/gitlab-org/gitlab-ce/issues/55221.

What are the relevant issue numbers?

Part of https://gitlab.com/gitlab-org/gitlab-ce/issues/55221.

Be aware of EE port https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/9389

Screenshots

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated via this MR
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• Security reports checked/validated by reviewer