Add examples for Logical models

[mj-h]

This PR adds examples for Logical models.

FSHOnline: https://fshschool.org/FSHOnline/#/gist/3973a248e20b8063c3e2cb8d35fa470b

I don't have a lot of experience with Logical models, especially the Characteristics keyword, but my example compiles without errors.

However, there is 1 warning: Type characteristics code system not found. Skipping validation of characteristics for PetAsResourceLikeObject..

[cmoesel]

Thanks for the example. We will take a look!

Regarding the warning, I looked into it and that happens because FSH Online does not auto-load the special hl7.fhir.uv.tools#current package. This is because FSH Online does not support #current packages right now. When I run your examples locally using SUSHI (not FSH Online), there is no warning.

[cmoesel]

This is a great example. I really like the way you walk through explaining logical models. And you stuck with the fish theme too! Fantastic!

Thank you for this. I've made one suggestion and pointed out one typo. Let me know what you think.

I also expected that our GitHub action would have automatically updated the index.json w/ this example, but it doesn't seem that happened. I'll look into that to see if I can figure it out.

[cmoesel]

This is great. Thank you for your contribution!

[jafeltra]

This new set of examples looks good to me. Thanks for contributing it!