[REQ] [Java] Upgrade to jackson 2.20.0

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

We're unable to consume jackson:2.20 in our Kotlin repo because of deprecations in this release that are not addressed in the latest version of openapi-generator.

For instance, openapi-generator auto-generates a file Serializer.kt that uses the deprecated function .setSerializationInclusion (docs):

object Serializer {
    @JvmStatic
    val jacksonObjectMapper: ObjectMapper = jacksonObjectMapper()
        .findAndRegisterModules()
        .setSerializationInclusion(JsonInclude.Include.NON_ABSENT)
        .configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false)
        .configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false)
}

Describe the solution you'd like

openapi-generator:7.15.0 still uses jackson:2.18.2. Request to upgrade to jackson:2.20.

Describe alternatives you've considered

• Continue to use older versions of jackson
• Look into alternatives to openapi-generator (which wouldn't be ideal)

Additional context

Start in pom.xml around the referenced Jackson dependency at line 1243, then inspect the generated Kotlin Serializer.kt example and the surrounding generator configuration. Update the dependency target to Jackson 2.20 and verify that generated output remains compatible with that release without the reported deprecated usage.