docs: public void substringField(String sourceField, String targetField, String from, String to) {
          TransformationStep step = new TransformationStep();
          step.setTargetField(targetField);
          step.setSourceFields(sourceField);
          step.setOperationParameter(TransformationConstants.SUBSTRING_FROM_PARAM, from);
          step.setOperationParameter(TransformationConstants.SUBSTRING_TO_PARAM, to);
          step.setOperationName("substring");
          steps.add(step);
      }