Add support for OpenAPI 3.2 main issue

[baywet]

OpenAPI 3.2 is out! and it's fully backward compatible with 3.1
This issue will detail the general rules of engagement, and I'll break the changelog OAI/OpenAPI-Specification#4600 into subsequent issues.

First off, all pull request should go to feat/oai-3-2-support on this repo. We'll then open up a PR upstream from that branch.

Second, I've added a kanban dashboard to track progress here OpenAPI 3.2 support (view)

[baywet]

Note: the release notes are now available here https://github.com/OAI/OpenAPI-Specification/releases/tag/3.2.0

[baywet]

WIP:

Missing:

• Headling - $self
• Data modeling - SSE
• Data modeling - multipart
• Data modeling - XML
• additional feature - security schemes
• additional feature - server object
• additional feature - propertyName optional
• additional feature - response object
• additional feature - media types components