feat(spring): enable `openApiNullable` with `useJackson3` #1152

Job	Run time
Build with JDK17 (samples/client/petstore/java-helidon-client/v3/mp/)	50s
Build with JDK17 (samples/openapi3/client/petstore/spring-cloud-3)	42s
Build with JDK17 (samples/client/petstore/spring-http-interface-reactive)	31s
Build with JDK17 (samples/server/petstore/springboot-x-implements-skip)	45s
Build with JDK17 (samples/client/petstore/spring-http-interface-noResponseEntity)	48s
Build with JDK17 (samples/client/petstore/spring-http-interface-reactive-noResponseEntity)	37s
Build with JDK17 (samples/client/petstore/java-helidon-client/v3/se)	50s
Build with JDK17 (samples/client/petstore/java/microprofile-rest-client-outer-enum)	57s
Build with JDK17 (samples/client/petstore/spring-http-interface)	35s
Build with JDK17 (samples/server/petstore/java-camel/)	1m 6s
Build with JDK17 (samples/client/petstore/spring-http-interface-useHttpServiceProxyFactoryInterfa...	37s
Build with JDK17 (samples/openapi3/server/petstore/springboot-3)	51s
Build with JDK17 (samples/server/petstore/java-helidon-server/v3/se)	52s
Build with JDK17 (samples/client/petstore/java/webclient-jakarta)	45s
Build with JDK17 (samples/server/petstore/java-helidon-server/v3/mp/)	48s
Build with JDK17 (samples/openapi3/server/petstore/springboot-3-include-http-request-context)	47s
	12m 21s

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