Update the Plan Stage page with VSA dogfooding

Why is this change being made?

1. Following the recent enhancement of adding VSA stage between MR label and MR merged events, we have new capabilities to measure the MR review time.
2. Optimize the MR review time will be a great Dogfooding showcase for VSA, and will increase the awareness about how to use it internally it in GitLab.
3. For groupoptimize using VSA internally is the best way to gather feedback for improvement.
4. Related also to https://gitlab.com/gitlab-org/plan/-/issues/753.

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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