Use json2python-models as a generalizer

[cmungall]

From discussion on slack with @ialarmedalien

json2python-models by @bogdandm can be seen as composing together generalization and python class generation

The generalization part could be used in place of our own generalize-json (but wired to output LinkML schemas) https://github.com/bogdandm/json2python-models

There are a number of advantages over our existing approach such as generalization to unions

There a few ways to approach this:

• Examine json2python-models and see if it's possible to call the generalization part to get an intermediate output
• Using json2python-models to create pydantic, then use the pydantic importer: #88