Add Agnes Slota as a backend maintainer

Manager Justification

• I have been working on the GitLab project for over 9.5 months as part of groupproject management team.
• I contributed to two Tier 2 initiatives, MVC1 and MVC2 of configurable work item statuses, which introduced highly requested customer features. Each MVC was rolled out behind feature flags to ensure smooth release.
• Since joining GitLab in January 2025, I have reviewed and approved over 130 MRs, including MRs outside groupproject management and MRs from community contributors.
• One month after joining GitLab, I became an internal backend reviewer for Plan Stage (devopsplan). By my second month, I became an official backend reviewer for the GitLab project.
• During my backend maintainer traineeship, which I started three months ago, I have reviewed more than 40 MRs. Here are examples of MRs I reviewed along with feedback from maintainers who reviewed after me. None of the MRs I approved have been reverted so far.
• As part of my backend maintainer traineeship, I also completed pairing sessions with three Staff Backend Engineers (@nicolasdular, @kassio, and @mksionek) from the groupproduct planning team. During these sessions, I was both shadowed while reviewing MRs from a maintainer’s perspective and had the opportunity to shadow a maintainer. These sessions provided valuable insights into different reviewing approaches and helped me improve the depth and quality of my own reviews.
• Throughout my traineeship, I have been mentored by backend maintainer @sdungarwal, who has supported me through the process by helping me set goals and sharing insightful guidance and feedback.

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

SPECIALITY 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 privately.
* 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 #backend_maintainers Slack channel
2. Remove yourself from maintainer_mentorship.yml and consider adding yourself as a maintainer mentor.
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 <project>/maintainers/backend with Owner access level.
5. Announce it everywhere
6. Familiarize yourself with documentation for Merging a merge request
7. Keep reviewing, start merging 🤘 😎 🤘