Argos visual regression tests

We use Argos CI to detect visual regressions on Docusaurus.

This workspace can be run manually, but is generally run through the Argos GitHub Action.

The workflow execute those following steps:

• Build the website locally with yarn build:website:fast
• Start the website server with yarn serve:website on http://localhost:3000
• Take screenshots of all pages found in sitemap.xml with Playwright
• Upload all screenshots to Argos CI

This workflow runs for main and PR branches, and add a commit status to each PR with a visual diff that we can easily inspect.

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Some additional capabilities:

• Use ./tests/screenshot.spec.ts to customize the screenshots we take, eventually filter out some useless sitemap pages like versioned docs
• Use ./tests/screenshot.css to hide flaky CSS elements: iframe, video, gif...