Set up website PR previews for Eclipse Sprotty

Summary

We are deploying https://github.com/eclipse-sprotty/sprotty-website to GitHub Pages. We would like to have the same solution for PR previews as it was recently done for the Langium website.

Priority

• Urgent
• High
• Medium
• Low

Severity

• Blocker
• Major
• Normal
• Low

Impact

PR previews are a very convenient way to see how the changes made in a PR would be reflected on the website.