Deploy tutorial as static MkDocs site to GitHub pages

[Karneades]

Add GitHub pages workflows to generate and deploy the tutorial as a static MkDocs site on GitHub pages.

The site is generated from the current markdown files and has

• Previous and Next buttons in the footer
• a simple side navigation
• a powerful search from MkDocs using the MkDocs theme materials.
• link to GitHub edit page from the individual pages
  • add buttons to jump quickly to GitHub for editing the page at hand
• workflow for building and deploying the site to the gh_pages branch directly after merge to master which is then pushed to the GitHub pages site as static site.

We can afterwards remove the "Next" links at the end of each file as this is obsolete with the Next button.

Demo: https://karneades.github.io/kubernetes-the-hard-way/

Closes #819