Distribution: adjust team merge request review SLO

Why is this change being made?

Our Distribution team MR review dashboard regularly reports many MRs breaching our documented SLO. Given that the amount of work coming to the team has increased significantly over time without additional headcount and technical debt payment to match, I want to propose we adjust our SLO to more reasonably reflect the team's capacity to address reviews.

I very much welcome any feedback on this. My goal here is to set a reasonable expectation both for Distribution team members as well as those requesting reviews from us.

Author Checklist

• Provided a concise title for this Merge Request (MR)
• Added a description to this MR explaining the reasons for the proposed change, per say why, not just what
  • Copy/paste the Slack conversation to document it for later, or upload screenshots. Verify that no confidential data is added.
• Assign reviewers for this MR to the correct Directly Responsible Individual/s (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 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 affect team members, or warrant an announcement in another way, please consider posting an update in #whats-happening-at-gitlab linking to this MR
  • If this is a change that directly impacts the majority of global team members, it should be a candidate for #company-fyi. Please work with internal communications and check the handbook for examples.

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