docs: make K8s tutorial fully match example charm

[dwilding]

This PR is a work in progress. Goals:

• Update command outputs to match what you get when playing the tutorial end to end
• Update the instructions about checking out the code:
  • Reference the examples directory instead of the juju-sdk-tutorial-k8s repo
  • Remind the reader to run charmcraft fetch-lib (in relevant chapters)
• Fix other small formatting/wording drive-bys

This PR follows on from #1719 and #1734. It also partially addresses #1653.