feat: Move Sec Principal Eng priorities to Development

Why is this change being made?

Per discussion in https://docs.google.com/document/d/1PS4BrTiPDanxhniCsvFbjnxYfZy73abjOGnAUlyFpes/edit we are moving the Sec Section Principal Engineer Priorities page from the Product handbook to Development.

For now the minimal change was keeping the existing priorites file around and changing CODEOWNERS. This file may get outdated quickly and/or be retired but it's still a very valuable input for me to maintain a list of cross-cutting priorities so I wanted to keep it around for the time being.

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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