Adding Quad Planning diagram

Why is this change being made?

I was Quad Planning my issues and realized there was a magic step on reviewing each issue in my process, so started trying to quantify what I look for as I review to make the process more consistent and reliable. As a visual learner, I did this by creating a mermaid diagram. I've added the diagram to the Quad Planning page to enable people to review and share their insights.

Author and Reviewer Checklist

Please verify the check list and ensure to tick them off before the MR is merged.

• 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
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  • 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
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  • The when to get approval handbook section explains the workflow in more detail
• For transparency, share this MR with the audience that will be impacted.
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