feat: Fix the issue where the JsonValue annotation cannot be used on an enum.

[shalousun]

public enum TrainJobType {
    TRAIN_TENSORFLOW_JOB( "train-tensorflow-job"),
    TRAIN_PYTORCH_JOB("train-pytorch-job");

    private final String value;

    TrainJobType(String value) {
        this.value = value;
    }
    @JsonValue
    public String getValue() {
        return value;
    }
}

• The @JsonValue annotation is applied to the getValue() method. This means that when an instance of TrainJobType is serialized to JSON, the value returned by getValue() is used.

• For example, if you serialize TrainJobType.TRAIN_TENSORFLOW_JOB, the resulting JSON would be train-tensorflow-job.