Update the Handbook to reflect changes to triage to include monitoring on MRs to the Customer Dot database

Why is this change being made?

Relates https://gitlab.com/gitlab-data/analytics/-/issues/16124

The Data team is responsible for pipelines that export the CDot database for Snowflake. Some database migrations in CustomersDot could impact this pipeline, leading to downtime. To prevent outages, Fulfillment engineers should request a review from a Data team member if an MR contains database changes. It's easy to forget to request a review, even if we add a checklist item to the MR template.

Through changes done via gitlab-org/customers-gitlab-com#5616 (closed), a new label will be added to MRs that introduce database changes in the customer-gitlab-com project and the data team needs to monitor these MRs.

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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