Codespaces and website docs

[agardnerIT]

This PR

• Reworks the docs in the walkthrough directory to be compatible with the codespaces / argo way of working
• Files in /docs will build the website
• mkdocs.yml is the metadata for the website

The site uses the mkdocs-macros-plugin plugin to allow the use of extras and thus "markdown include variables" such as {{ foo }} being dynamically replaced by looking up:

mkdocs.yml

extras:
 foo: "bar"

Note: Merging this PR won't be enough to have a functioning website.
The GitHub Action will take the .md files from /docs and transform to HTML then create and push to gh-pages branch.

The repo admin needs to go into the repo settings and set up GitHub pages to build from the gh-pages.

Only then will a website be available. I believe the URL will be: https://dynatrace-oss.github.io/progressivedelivery-masterclass

[heckelmann]

That's great @agardnerIT!

Maybe you can check on your environment Grafana?
It seems like the issue with grafana and the forwarded ports in codespaces is gone and the origin not allowed-Error solved, so we would not need the GH CLI anymore.