Make pedropombeiro backend maintainer of GitLab

Overview

This is ongoing issue to track my reviews. It's not submitted for approval yet, just for history purposes so it's easier to get "example of reviews" and "latest reviews".

I am now ready to apply for maintainership, having reviewed 203 MRs (195 merged) in gitlab-org/gitlab after I started working on the codebase in mid 2021. I've tracked ~37 reviews in this MR, 21 of which were merged as-is.

Review template

For maintainer: this review is part of [my maintainership trainee program](https://gitlab.com/gitlab-com/www-gitlab-com/-/merge_requests/113988). Any feedback is appreciated.

<details>
<summary>Why I think this MR is ready for merge</summary>

* ...
* Changelog entry is ...
* MR complies to our backend review guidelines

</details>

Examples of reviews

Things to improve

@gitlab-org/maintainers/rails-backend please chime in below with your thoughts, and approve this MR if you agree. Keep in mind this advice from the handbook:

Normal non-blocking feedback should be submitted as comments to the MR. To support GitLab Values and avoid groupthink, any blocking negative feedback should be instead submitted to the manager of the aspiring maintainer. The manager will then share the feedback with the aspiring maintainer and post a generic message with a "TL;DR" in the MR.

Maintainer review checklists

• GraphQL MR reviews
• Database MR reviews

Developer checklist

• Before this MR is merged
  • Mention ATgitlab-org/maintainers/rails-backend, if not done (this issue template should do this automatically)
  • Assign this issue to your manager
• After this MR is merged
  • Consider adding 'backend maintainer' to your Slack notification keywords
  • Add yourself to the #backend_maintainers slack channel

Manager checklist

• Before this MR is merged
  • The MR has been open for 5 working days
  • 5 existing maintainers approve the MR (see the maintainer list)
  • There are no blocking concerns raised (if there are, please follow https://about.gitlab.com/handbook/engineering/workflow/code-review/#how-to-become-a-project-maintainer)
• After this MR is merged
  • Announce the good news in the relevant channels listed in https://about.gitlab.com/handbook/engineering/#keeping-yourself-informed