docs: create Docusaurus v2.2.0 release docs + changelog + release blog post

[slorber]

Motivation

Add 2.2.0 docs version + backport all docs changes from commits backported for the 2.2 release

Code is backported here: #8264

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New/updated docs have been successfully backported with this command:

git format-patch -k --stdout v2.1.0...slorber/docusaurus-v2.2-backport -- website/docs | sed 's,a/website/docs,a/website/versioned_docs/version-2.2.0,g ; s,b/website/docs,b/website/versioned_docs/version-2.2.0,g' | git apply

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Preview links:

• https://deploy-preview-8265--docusaurus-2.netlify.app/blog/releases/docusaurus-2.2
• https://deploy-preview-8265--docusaurus-2.netlify.app/changelog/2.2.0/
• https://deploy-preview-8265--docusaurus-2.netlify.app/docs/2.2.0/

[netlify]

✅ [V2]

Name	Link
🔨 Latest commit	5889235
🔍 Latest deploy log	https://app.netlify.com/sites/docusaurus-2/deploys/635d03b7451171000af6deac
😎 Deploy Preview	https://deploy-preview-8265--docusaurus-2.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

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[github-actions]

⚡️ Lighthouse report for the deploy preview of this PR

URL	Performance	Accessibility	Best Practices	SEO	PWA	Report
/	🟠 72	🟢 97	🟢 100	🟢 100	🟢 90	Report
/docs/installation	🟠 75	🟢 100	🟢 100	🟢 100	🟢 90	Report

[github-actions]

Size Change: +53.1 kB (+6%) 🔍

Total Size: 872 kB

Filename	Size	Change
website/.docusaurus/globalData.json	67 kB	+14.4 kB (+27%)	🚨
website/build/assets/css/styles.********.css	112 kB	+200 B (0%)
website/build/assets/js/main.********.js	652 kB	+38.4 kB (+6%)	🔍
website/build/index.html	40.9 kB	+63 B (0%)

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