[BUG] specifying jackson serialization in configOptions for java generation still uses gson

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• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
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Description

I would like to use jackson instead of gson for serialization when generating the java openapi client.
In configOptions in the generateJavaClient task, I have:

task generateJavaClient(type: org.openapitools.generator.gradle.plugin.tasks.GenerateTask) {
    group = 'OpenAPI Tools'
    description = 'Generates a Java SDK client to connect to this service'
    generatorName = "java"
    inputSpec = "$rootDir/open-api/alert-service-api-spec.yml".toString()
    outputDir = "$buildDir/generated/java".toString()
    apiPackage = "com.thousandeyes.alert.sdk.api"
    invokerPackage = "com.thousandeyes.alert.sdk.invoker"
    modelPackage = "com.thousandeyes.alert.sdk.model"
    configOptions = [
            library: "retrofit2",
            serializationLibrary: "jackson", // this does not seem to be honors. Still uses Gson.
            dateLibrary         : "java8"
    ]
}

openapi-generator version

I am using version 6.2.0. I don't know if it is a regression or not.

OpenAPI declaration file content or url

N/A

Generation Details

I got the same generated code (using gson serialization) whether serializationLibrary: "jackson" is specified or not.

Steps to reproduce

Run ./gradlew generateJavaClient

Related issues/PRs

Suggest a fix

Generated code should use jackson instead of gson.

Start by running ./gradlew generateJavaClient with the shown configOptions, then trace how the Java generator handles serializationLibrary for the retrofit2 library. Done means the generated client uses Jackson serialization instead of Gson when serializationLibrary is set to "jackson".