Expand Gemfile/MissingFeatureCategory custom categories to have a QA category

Context

See initial discussion.

Having a custom category for the Quality department would be useful for defining the ownership of QA-related gems (e.g. !132902 (diffs)).

Goals

• Extend https://gitlab.com/gitlab-org/gitlab/-/blob/7bd3b8a785be23ca1167ea0a154277f6b5159a63/rubocop/feature_categories.rb#L19-25 to have a feature category for the Quality department.
• (Optional, but appreciated) Create a follow-up MR to add some QA-related gems (example) to this new feature category