[REQ] Support for OpenAPI Spec 3.1

Created by: westn

Is your feature request related to a problem? Please describe.

Support for OpenAPI Spec 3.1, released last month: https://github.com/OAI/OpenAPI-Specification/releases/tag/3.1.0

Describe the solution you'd like

Add support for OpenAPI Spec 3.1

Additional context

Couldn't see any other mention of this besides a short mention in #15 Another note on https://www.openapis.org/blog/2020/06/18/openapi-3-1-0-rc0-its-here which mention that the specification-change is bigger than it sounds and might break some tooling.