Add conclusions chapter to Kubernetes charm tutorial

[dwilding]

It would be helpful to add a "conclusions" chapter K8s tutorial with pointers about how to publish the charm and suggestions for what to do next (e.g., other functionality to add to the charm).

[dwilding]

I've scoped out the items that were previously listed in this issue. Thanks @tonyandrewmeyer for your help! My planned sequence of work is:

1. #1718
2. Add a conclusions chapter (this issue)
3. Switch charmcraft profiles to use uv, Jubilant, and charmcraft test
4. #1749

[dwilding]

Merging #1716 into this issue. Capturing Tony's description:

The tutorial currently ends fairly abruptly. It would be good to add a concluding (congratulatory) note, and point the user to potential next steps, including charm publishing (linking to the charmcraft docs), and perhaps the manage charms how-to.