Add reviewer values

Why is this change being made?

See: gitlab-org/gitlab!57293 (merged)

A MVC for: gitlab-org/frontend/rfcs#86 (closed)

Define a set of Values to deliver maintainer reviews from. This is not a set of rules but rather, a guiding set of principles for maintainers to lean into for consistency in our reviews with one another, much in the same way we have values for delivering code and conduct here in GitLab: https://about.gitlab.com/handbook/values/

Relates to: gitlab-org/frontend/frontend-managers/initiatives#29 (closed)

This work is being broken into two efforts:

Merge	You are here
Add reviewer values	🤘
Add/update reviewer implementation guidelines(breaking down merges, deferring to subject experts, keeping iteration high, acting through collaboration and other proven successful methods to reduce cycle time for reviews)	TBA

Author Checklist

• Provided a concise title for the MR
• Added a description to this MR explaining the reasons for the proposed change, per say-why-not-just-what
• Assign this change to the correct DRI
  • If the DRI for the page/s being updated isn’t immediately clear, then assign it to one of the people listed in the "Maintained by" section in on the page being edited.
  • If your manager does not have merge rights, please ask someone to merge it AFTER it has been approved by your manager in #mr-buddies.
  • If the changes relate to any part of the project other than updates to content and/or data files please make sure to ping @gl-static-site-editor in a comment for a review and merge. For example changes to .gitlab-ci.yml, JavaScript/CSS/Ruby code or the layout files. (this requirement has been removed pending identification of a new DRI for the handbook)