OpenAPI: Nullable support

[jay-babu]

Is your feature request related to a problem? Please describe.
A clear and concise description of what the problem is.
Ex. I'm always frustrated when [...]

Describe the solution you'd like
Looking for a way to support PATCH spec which requires knowing the tri-state. Is there a way that this could be supported with https://github.com/oapi-codegen/nullable/tree/main

Describe alternatives you've considered
Did not see docs on this