Add dstull as frontend maintainer of gitlab project

Manager Justification

It's hard to specify hard requirements for becoming a maintainer, which is why the documentation consists of flexible guidelines. Reviewers are encouraged to think of their eligibility for maintainership in the terms of "I could be ready at any time to be a maintainer as long as it is justified".

• 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.

Doug has been a backend maintainer for the GitLab project since 2021 and has consistently demonstrated deep technical expertise across the codebase. His decision to pursue frontend maintainership reflects his commitment to full-stack ownership and his team's needs.

Since starting this journey towards maintainership, catalogued in frontend maintainer trainee issue, Doug has completed 50+ frontend reviews. His reviews demonstrate:

Breadth of expertise: Doug has reviewed a wide variety of frontend changes including Vue components, GraphQL migrations, styling updates, accessibility improvements (!204414), and complex state management implementations. His reviews show comfort across the entire frontend stack, with maintainers noting he performs both backend and frontend reviews effectively.

Quality and thoroughness: Maintainers consistently praise his review quality. @aturinske noted: "It was a thorough review and I liked your penchant for non-blocking actions (both comments and follow-up issues). It kept the review fast and on track." His reviews catch issues that would otherwise require maintainer intervention, such as identifying misconfigured translations, unnecessary code patterns, and CE/EE separation concerns (!193826, !188312).

Balanced iteration approach: Doug provides clear, actionable feedback that balances iteration with quality. He frequently uses non-blocking suggestions and creates follow-up issues for improvements, keeping MRs moving while ensuring quality standards. @kpalchyk noted: "I think @dstull did a great review, highlighting concerns on CE/EE code separation, and suggesting options to resolve the issue."

Cross-functional expertise: His reviews demonstrate understanding of accessibility, UX considerations, testing best practices, and architectural patterns. @anna_vovchenko praised his ability to perform both backend and frontend reviews on the same MR (!204072).

Consistency: Doug's authored MRs demonstrate the same high quality he expects in reviews - they consistently pass through reviewer and maintainer review with minimal required changes.

As Doug's manager, I'm confident his track record in his trainee issue demonstrates readiness for frontend maintainership. His backend maintainer experience, combined with his demonstrated frontend expertise and consistent positive feedback from current maintainers, makes him well-positioned to provide holistic technical guidance across the stack.

Before Merging (Manager Tasks)

• Close any relevant trainee maintainer issues with a comment indicating that this merge request is being created, as (they are no longer required to become a maintainer).
• Mention the maintainers from the given specialty with the template below and ask them to provide feedback to the manager directly. Emphasize that any negative feedback should be communicated privately to the manager/mentor, not in the merge request, as outlined in our maintainership feedback documentation.
• Leave this merge request open for 1 week, to give the maintainers time to provide feedback.
• Check this box to confirm that you approve the access provision.
• Ensure we have at least 2 approvals from existing maintainers.

Template call to action

`@gitlab-org/maintainers/frontend` Maintainers, please review this proposal to make TRAINEE maintainer of PROJECT.

* If you have blocking feedback adhering [to the documentation](https://handbook.gitlab.com/handbook/engineering/workflow/code-review/#request-maintainership-feedback) please share it with me.
* If you are in agreement, and can vouch for this proposal, please approve.

After 1 week, if there is no blocking feedback and at least 2 approvals, I will merge this MR.

Once This MR is Merged

1. Join the [at]frontend-maintainers slack group
2. Let a maintainer add you to <project>/maintainers/frontend with Owner access level.
3. Announce it everywhere
4. Familiarize yourself with documentation for Merging a merge request
5. Keep reviewing, start merging 🤘 😎 🤘