add more semantics to LinkML model

[lopierra]

• type Any: https://linkml.io/linkml/schemas/advanced.html#linkml-any-type - I think this means you can add arbitrary metadata key:value pairs
• any_of: https://linkml.io/linkml/schemas/advanced.html#linkml-any-type (e.g. enum for a variable OR missing-value enum)
• inlining: https://linkml.io/linkml/schemas/inlining.html
• reusing slots:
  • https://linkml.io/linkml/intro/tutorial07.html#customizing-slots-in-the-context-of-classes-slot-usage
  • https://linkml.io/linkml/schemas/slots.html#slot-usage