[SPRING] support option `openApiNullable` with `useJackson3`

[sonallux]

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

Currently it is not possible to use the option openApiNullable together with useJackson3 and useSpringBoot4:

java.lang.IllegalArgumentException: openApiNullable cannot be set with useJackson3
    at org.openapitools.codegen.languages.SpringCodegen.processOpts (SpringCodegen.java:499)
    ....

Describe the solution you'd like

Support the option openApiNullable together with useJackson3 and useSpringBoot4. The missing Jackson 3 support on jackson-databind-nullable hast just been released with Version 0.2.10 (see PR
OpenAPITools/jackson-databind-nullable#117).

Describe alternatives you've considered

Additional context

The initial support for Spring Boot 4 and Jackson 3 was implemented in PR #22854. This PR also introduced the constraint, that openApiNullable is not allowed.