feat: generate schema from example message

dalelane commented 3 months ago

The generator has been implemented assuming that all message objects include a payload with properties. This is used when generating Java classes to be able to create attributes that matching the expected message properties.

This causes the generator to fail with AsyncAPI documents that don't include payload properties. Some such documents will provide a sample message instead. For these documents, we can attempt to derive a schema from the sample, and use that schema to generate a usable set of properties.