Refresh K8s charm tutorial, with source files in Ops repo

[dwilding]

This issue is for tracking several related improvements to the Kubernetes charm tutorial:

1. Do a clean play through of the tutorial and fix/clarify any inconsistencies.
2. Put the charm files in the Ops repo, in a new directory called examples.
   • Have a directory corresponding to the charm files as of the end of each chapter.
   • Add a CI workflow that runs the unit tests in each directory.
3. Decide what to do with FastAPI-Monitoring.json.tmpl, which is referenced in the last chapter of the tutorial.
4. Archive the juju-sdk-tutorial-k8s repo.
   • At the end of each chapter, link to the relevant directory within examples.