Add a CTO Staff page to the Engineering handbook

Why is this change being made?

This allows us to reduce the size of the main Engineering page slightly. Currently the new page has details on:

1. The weekly Engineering Staff Meeting.
2. The Acting Chief of Staff to the CTO rotation.

In future, it will also contain information about Engineering offsites.

Review app: https://add-cto-staff-page.about.gitlab-review.app/handbook/engineering/cto-staff/

Part of chief-of-staff-cto#2.

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
  • Copy/paste the Slack conversation to document it for later, or upload screenshots. Verify that no confidential data is added.
• Assign reviewers for this change to the correct DRI(s)
  • 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.

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