writes multiinstance_sequential:'Yes' in JSON output

the old BaseBpmnJsonConverter.convertToJson() does not write 'multiinstance_sequential' property when the value is 'true', which causes JsonConverterUtil.getPropertyValueAsBoolean(PROPERTY_MULTIINSTANCE_SEQUENTIAL, elementNode) returns default value 'false' in BaseBpmnJsonConverter.convertToBpmnModel() method:

  public static boolean getPropertyValueAsBoolean(String name, JsonNode objectNode, boolean defaultValue) {
    boolean result = defaultValue;
    String stringValue = getPropertyValueAsString(name, objectNode);
    
    if (PROPERTY_VALUE_YES.equalsIgnoreCase(stringValue)) {
      result = true;
    } else if (PROPERTY_VALUE_NO.equalsIgnoreCase(stringValue)) {
      result = false;
    }
    
    return result;
  }