Add msaleiko as backend maintainer

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 my work as an author and reviewer is consistent with other maintainers".

• The MRs reviewed by the candidate consistently make it through maintainer review without significant additionally required changes.
  • Convert RefMatcher specs to shared_examples (gitlab-org/gitlab!157298 - merged)
  • Fix two feature specs (gitlab-org/gitlab!156480 - merged)
  • Create new custom Permission: read_crm_contact (gitlab-org/gitlab!154017 - merged)
  • Enfore 100 child limit (gitlab-org/gitlab!151656 - merged)
  • https://gitlab.com/gitlab-org/security/gitlab/-/merge_requests/4010
  • Bump kas-grpc gem to 0.5.0 (gitlab-org/gitlab!150416 - merged)
  • Removing condition disabling iterations on issu... (gitlab-org/gitlab!148306 - merged) Community contribution
  • Adding edit AI Agent page (gitlab-org/gitlab!145719 - merged)
  • Failing entity if pipeline aborts on failure (gitlab-org/gitlab!136512 - merged)
  • Deprecate UpdateRepositoryStorageWorker arguments (gitlab-org/gitlab!136242 - merged)
• The MRs authored by the candidate consistently make it through reviewer and maintainer review without significant required changes.
  • Convert to ticket quick action respects default... (gitlab-org/gitlab!157025 - merged)
  • Adds type to issue webhook attributes (gitlab-org/gitlab!156760 - merged)
  • Adds List-Unsubscribe-Post header to notificati... (gitlab-org/gitlab!156414 - merged)
  • Adds templating functionality to new participan... (gitlab-org/gitlab!151799 - merged)
  • Rename /invite_email quick action to /add_email (gitlab-org/gitlab!151776 - merged)
  • Adds Service Desk new participant email (gitlab-org/gitlab!150706 - merged)
  • Adds tickets_confidential_by_default to control... (gitlab-org/gitlab!150492 - merged)
  • Support X-Original-To headers for email ingestion (gitlab-org/gitlab!149874 - merged)
  • Add system note when external participant unsub... (gitlab-org/gitlab!142287 - merged)
  • Adds convert_to_ticket quick action (gitlab-org/gitlab!139553 - merged)

@msaleiko has reviewed over 70 merged MRs and authored over 180 merged MRs. He's been with GitLab for 1.75 years and started reviewing about a year ago (due to being in the Incubation Engineering Department before) and recently joined the devopsplan stage and the groupproject management team.

• Passes on context when he has further domain knowledge on how to improve the MR or make the code easier 1, 2
• Cares about potential performance pitfalls 1
• Focuses on code quality 1, 2
• Ensure the UI looks good 1
• Ensures metadata is correct 1, 2, 3, 4, 5, 6
• Encourages code readability and re-use existing code when possible 1, 2, 3
• Identifies missing test cases and improves test case quality 1, 2, 3, 3, 4, 5, 6, 7

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.
• 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.

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://about.gitlab.com/handbook/engineering/workflow/code-review/#how-to-become-a-project-maintainer) please share it with me via Slack.
* 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. Ask the maintainers in your group to invite you to any maintainer-specific meeting if one exists.
3. Let a maintainer add you to @gitlab-org/maintainers/rails-backend with Owner access level.
4. Announce it everywhere
5. Familiarize yourself with documentation for Merging a merge request
6. Keep reviewing, start merging 🤘 😎 🤘