test: add visual regression tests with Argos CI

[slorber]

Motivation

argos-ci.com has been useful for upgrading to MDX 2, where I used Argos through a separate repo (https://github.com/slorber/docusaurus-visual-tests)

We decided to install it on the Docusaurus repo to generalize the idea and benefit from visual regression tests on all PRs.

The current setup:

• builds the website locally
• takes website screenshots with Playwright for all sitemap pages
• upload all the screenshots to the Argos SaaS

This runs on main and on PR branches and generates a visual diff to inspect on each PR

[netlify]

✅ [V2]

Name	Link
🔨 Latest commit	b874493
🔍 Latest deploy log	https://app.netlify.com/sites/docusaurus-2/deploys/644bcd52616ae700081685b2
😎 Deploy Preview	https://deploy-preview-8947--docusaurus-2.netlify.app
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[github-actions]

⚡️ Lighthouse report for the deploy preview of this PR

URL	Performance	Accessibility	Best Practices	SEO	PWA	Report
/	🟠 85	🟢 97	🟢 92	🟢 100	🟠 89	Report
/docs/installation	🟠 75	🟢 100	🟢 92	🟢 100	🟠 89	Report

[github-actions]

Size Change: 0 B

Total Size: 1.01 MB

ℹ️ View Unchanged

Filename	Size
website/.docusaurus/globalData.json	101 kB
website/build/assets/css/styles.********.css	113 kB
website/build/assets/js/main.********.js	752 kB
website/build/index.html	41.3 kB

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