Improve clarity of diagnosis example

[jmsfltchr]

What is the goal of this PR?

Reformat the diagnosis example to make it as clear as possible to users how they can build their own KGCN.

What are the changes implemented in this PR?

• Move main parameters to be easily visible
• Move out generic util methods for retrieving types and roles
• Improved docstrings
• Some outdated format docstrings updated to Google format