Add support for jackson-databind-nullable

[noshua]

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

When using springdoc-openapi together with openapi-generator and it's jackson-databind-nullable the generated swagger-ui for nullable fields is broken. Instead of showing the Object attributes only "present": true is displayed.

Describe the solution you'd like

A JsonNullable<Object> attribute should be displayed like an Optional<Object>. So the Object attributes should be displayed.

Describe alternatives you've considered

And couldn't find any alternatives.

Additional context