Update j_lar to be gitlab backend maintainer

• I have completed over 150 reviews
• I have tracked my recent reviews in a trainee issue

Review examples

• Found bugs 1 2
• Helped make the specs a little cleaner
• Helped make the spec output easier to consume in case of a failure
• Suggested a more helpful example
• Found misleading test case titles

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.
• The MRs authored by the candidate consistently make it through reviewer and maintainer review without significant required changes.

On top of doing reviews consistently and with a high quality as outlined above, @j_lar has also been a reviewer for "analytics instrumentation" and authored complex and important changes such as:

• New features:
  • Add total count metrics to Gitlab Internal Events (gitlab-org/gitlab!129618 - merged)
  • Create module for Internal Events (gitlab-org/gitlab!142658 - merged)
• Test performance optimisations:
  • Only validate metrics definitions with test to ... (gitlab-org/gitlab!134115 - merged)
• Migrating tracking code:
  • Migrate i_code_review_create_mr to total counts (gitlab-org/gitlab!138030 - merged)

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 🤘 😎 🤘