Not to include StepExecution persistentUserData in StepExecutionEntity in rest api

javax.batch.runtime.StepExecution#getPersistentUserData returns java.io.Serializable, which may not be human readable.

When the persistent user data is a custom type provided by application, the client side may not have the class to deserialize it.

Even the batch runtime may not have the class to properly deserialize it when javax.batch.runtime.StepExecution#getPersistentUserData() is called. The application that had created that persistent user data may not be present.