Add examples that can be used by MkDoc

MkDoc can embed examples in the LinkML class documentation
https://linkml.io/linkml/generators/docgen.html

Examples can optionally be integrated into the documentation; to enable this, pass in the –example-directory argument. The example directory should contain one file per example, following the naming convention -..

For example, to include examples on the page for Person, include examples

Person-001.yaml, Person-002.yaml, etc.

Currently examples must be in yaml

MkDocs option:
example-directory
Folder in which example files are found. These are used to make inline examples

Start with the linked LinkML generator documentation and the MkDocs `example-directory` option. Identify the repository’s documentation or example entry points, then add examples using the `-.` naming convention; done means YAML examples are discovered and rendered inline in the class documentation.

Written by the indexing model from the issue text.