Add mergeable requirements for MRs to CEO MR reviews handbook

Why is this change being made?

Requesting an MR review from the CEO needs to be efficient, with all requirements prepared. Suggested in Slack (internal), this MR adds details about the mergeable status of an MR, no unresolved comment threads, MR draft removed (marked as ready) and the CI/CD pipeline ran successfully and the review app is deployed. Documentation URLs are included to ensure everyone can learn and contribute.

In addition, this MR adds a copy-paste quick action for assigning Sid as a reviewer when requestors prepare everything.

Related to adding the MR review workflow MR: !106957 (merged)

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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