misc: move lighthouse message formatter to admin folder, refactor

[Josh-Cena]

Pre-flight checklist

• I have read the Contributing Guidelines on pull requests.
• If this is a code change: I have written unit tests and/or added dogfooding pages to fully verify the new behavior.
• If this is a new API or substantial change: the PR has an accompanying issue (closes #0000) and the maintainers have approved on my working plan.

Motivation

Moved it to admin/scripts, so that it can be linted.
Refactored it to use TypeScript + ESM.
Should make it more DRY and less likely to break when API changes?

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[github-actions]

⚡️ Lighthouse report for the changes in this PR

URL	Performance	Accessibility	Best Practices	SEO	PWA	Report
/	🟠 60	🟢 100	🟢 100	🟢 100	🟢 90	View report
/docs/installation	🟠 85	🟢 96	🟢 100	🟢 100	🟢 90	View report