OpenApi 3.1 and JSON Schema support

https://apisyouwonthate.com/blog/openapi-v3-1-and-json-schema/

Looks like openapi 3.1 and JSON schema Draft 2020-12 have been brought together.
We should check we support 3.1 and JSON Schema for type generation, as it looks like some changes have been made from 3.0.

Start by reviewing the repository's existing OpenAPI 3.0 and JSON Schema type-generation support, then compare it with OpenAPI 3.1 and JSON Schema Draft 2020-12 using the linked reference. Done means the project’s support for the newer specifications has been checked and the required type-generation changes are identified and covered.

Written by the indexing model from the issue text.