code: public Attachment attachUrl(long sheetId, Attachment attachment) throws SmartsheetException
      {
          return this.createResource("sheets/" + sheetId + "/attachments", Attachment.class, attachment);
      }
docs: Attach a URL to a sheet.
  
  The URL can be a normal URL (attachmentType "URL"), a Google Drive URL (attachmentType "GOOGLE_DRIVE") or a
  Box.com URL (attachmentType "BOX_COM").
  
  It mirrors to the following Smartsheet REST API method: POST /sheets/{sheetId}/attachments
  
  @param sheetId the sheet id
  @param attachment the attachment object
  @return the attachment object
  @throws IllegalArgumentException if any argument is null or empty string
  @throws InvalidRequestException if there is any problem with the REST API request
  @throws AuthorizationException if there is any problem with  the REST API authorization (access token)
  @throws ResourceNotFoundException if the resource cannot be found
  @throws ServiceUnavailableException if the REST API service is not available (possibly due to rate limiting)
  @throws SmartsheetException if there is any other error during the operation