Add Coung Ngo as GitLab frontend maintainer

Manager Justification

• The MRs reviewed by the candidate consistently make it through maintainer review without significant additionally required changes.
• The MRs authored by the candidate consistently make it through reviewer and maintainer review without significant required changes.

@cngo has been at GitLab for just over three years. In that time, he's contributed and assisted in a large number of MRs. He's excellent at providing feedback and has the technical knowledge we expect from someone maintaining our codebase. After reviewing a number of his recent reviews, I am proposing that we make him a maintainer of the GitLab frontend codebase.

• Has been a Senior Frontend Engineer for over a year
• Has authored more than 525 merge requests.
• Has reviewed and approved over 740 merge requests
• Reviewed over 80 community contributions.
• Went through the legacy Trainee maintainer process.

Before Merging(Manager Tasks)

• Mention the maintainers from the given specialty and ask them to provide feedback directly on this merge request.
• Leave this merge request open for 1 week, to give the maintainers time to provide feedback.
• Ensure we have at least 2 approvals from existing maintainers.

Once This MR is Merged

1. Create an access request for maintainer access to gitlab-org/<project>.
2. Join the [at]frontend-maintainers slack group
3. Ask the maintainers in your group to invite you to any maintainer-specific meeting if one exists.
4. Let a maintainer add you to gitlab-org/maintainers/frontend
5. Announce it everywhere
6. Keep reviewing, start merging 🤘 😎 🤘