PTransform for serializing objects to JSON Strings.AsJsons PTransform that will transform a PCollection<InputT>
into a PCollection of JSON Strings representing those objects using a
Jackson ObjectMapper.ParseJsons PTransform that will parse JSON Strings
into a PCollection<OutputT> using a Jackson ObjectMapper.PTransform for parsing JSON Strings.ObjectMapper instead of the default one.ObjectMapper instead of the default one.