refactor: use Remark to parse Markdown on server-side

[Josh-Cena]

Motivation

Replaces #5670

Fixes #6260
Fixes #6108
Fixes #5659

Have you read the Contributing Guidelines on pull requests?

Yes

Test Plan

TODO

[netlify]

✔️ [V2]

🔨 Explore the source changes: ae9de69

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[github-actions]

⚡️ Lighthouse report for the changes in this PR:

Category	Score
🟠 Performance	71
🟢 Accessibility	98
🟢 Best practices	100
🟢 SEO	100
🟢 PWA	95

Lighthouse ran on https://deploy-preview-6261--docusaurus-2.netlify.app/

[github-actions]

Size Change: 0 B

Total Size: 755 kB

ℹ️ View Unchanged

Filename	Size
website/.docusaurus/globalData.json	47 kB
website/build/assets/css/styles.********.css	105 kB
website/build/assets/js/main.********.js	573 kB
website/build/index.html	30.1 kB

_{compressed-size-action}

[Josh-Cena]

There is a performance degradation. On CHANGELOG.md, our previous early-bail-out algorithm runs for 2.9ms; the current one runs for 450ms. We certainly need to find a lazy-evaluated parser. Note however that on smaller files the time is still negligible (some 10ms–40ms) and our CHANGELOG.md isn't really current parsed server-side anyways