openapi 3.1 - support json schema dialect for openapi schemas

[chrisradek]

Open API 3.1 schemas are a superset of Json Schema draft 2020-12. This is different from Open API 3.0 where Open API schemas only supported a subset of draft-06 (while also including some metadata like nullable instead of using type: "null")

This issue tracks updating/creating the Open API 3.1 schema emitter to target Json Schema 2020-12.

This will involve

• Creating JSON Schema 2020-12 types that the Open API 3.1 schema type can reference
• Creating an Open API 3.1 schema emitter that targets the Open API 3.1 schema types