add CI pipeline and deploy workflow for GitHub Pages

[uli-f]

This adds a very simple ci workflow and a deploy workflow.

• CI runs on PR from source and push to source, but can also be triggered manually from Actions tab
• CI workflow adds the output of npm run production to the workflow (example)
• deploy to github pages can be manually run from Actions tab (I cannot see the Run workflow button, that might be either permissions related or we have to merge to main (=source) first)
  
• deploy to github pages will also run when releasing thru GitHub

In the repo Settings | Pages I changed the Source from Deploy from a branch to GitHub Actions:

I could not test the actual deploy workflow. Might be best to merge this and then run it manually from Actions tab.

[johnmay]

Awesome