update MR rate definition and troubleshooting steps

Why is this change being made?

Update MR Rate in metrics page to reflect more accurate definition and how to troubleshoot.

Merge Request (MR) Rate is a measure of productivity and efficiency. The numerator is a collection of merge requests to a set of projects. The denominator is a collection of people based on the job title specialty field in Workday. Both are tracked over time (usually monthly). The stages.yml file is the SSOT for group names. We rely on a mapping between the group name in this file to the job title specialty field in Workday. A mismatch between the two would cause team members or MRs not to be counted.

In April 2023, there was an internal audit of the job title specialty field done by managers and directors. MR Rate data prior to this date may report inaccuracies due to missing or incorrect job title specialities that were corrected in the audit.

You can use this MR Rate troubleshooting dashboard to check the number of team members that are counted each month. If the monthly team member count is less than expected, refer to the table to see which team member is missing.

To update the job title speciality field, please refer to the guidelines.

Related to gitlab-org/quality/engineering-analytics/team-tasks#205

Closes gitlab-org/quality/engineering-analytics/team-tasks#224

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, and the content is SAFE
• 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
  • The when to get approval handbook section explains the workflow in more detail
• 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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