Support OpenAPI version 3.2

[pieterocp]

As the the big release announcement in September 2025, some of the features might be nice to add in.

Personally, the feature I'd most like is the query method, but there's a bunch of additions to the specification in there.

Think that it might be possible to not have too many changes to support 3.0, 3.1 and 3.2 but the codebase + tests will surely humble us.

Further reading: https://spec.openapis.org/oas/v3.2

Schema creation upgrade guide - https://learn.openapis.org/upgrading/v3.1-to-v3.2.html