Draft: docs(codeowners): add Dan MH as pajamas maintainer

This MR follows [time] working on my trainee maintainer issue.

Larger efforts

Dan has consistently helped guide numerous large additions to Pajamas during his trainee process, during which his deep knowledge of all design system work was very evident. Here are some highlights:

• Provided feedback on a number of large additions to Pajamas documentation, including adding stepper, headings scale, combobox and design token docs.
• Added embedded examples for numerous components (example 1, example 2) and cleaned up a number of structure images (example 1, example 2, more examples).
• Updated maintainer docs to increase consistency of reviews.

Maintainer-level reviews

Dan consistently asks great questions and generates useful debate in his reviews. Here are some examples (two are still in progress, but left in the list as they are great examples of Dan's reviews and contributions:

• Considerations to principles !3785 (merged)
• Use gl-heading styles !3707 (merged)
• Make button group its own page !3774
• Standardize delay timing !3512 (merged)
• Suggest ellipsis box for truncation !3625 (merged)
• Clarify palette and concepts !3646 (merged)
• Add image and graphic notes !3534 (merged)
• Add drawer title size spec !3536 (merged)
• Add feedback animation guidelines !3729 (merged)

(Full list of reviews on my trainee maintainer issue)

Things I want to continue working on

• Help teams work faster together by
  • Making the design system easier to use
  • Improve the components, tools, and assets to make building GitLab more efficient
  • Reduce inconsistencies and contradictions between the multiple sources of truth
• As part of groupdesign system
  • Explore ways for feature teams to initiate changes, additions, to the design system
  • Refine the definitions of what should and shouldn't be part of Pajamas
  • Identify and abstract patterns already in use across GitLab, getting them ready for the design system