Docusaurs: Modify GitHub actions to build & test

[Jwaegebaert]

Update the GitHub Actions to accommodate Docusaurus.

• Modify the test_docs job in Check PR
• Modify the test_docs job in Release
• Modify the test_docs and deploy_docs jobs in Release next

https://docusaurus.io/docs/deployment#triggering-deployment-with-github-actions

Note!

When making a PR for this issue, make sure you target the branch docs-migration.

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Related to #4396