HPCC-12591 Add new method WsWorkunits.WUGetStats

GetStatsFormat: 'xml' or 'json', default 'xml';
GetStatsOption:
  default or 0 -> return stats data in specified format;
  1 -> download stats data as an file;
  2 -> download stats data as a ZIP file;
  3 -> download stats data as a GZIP file.

Signed-off-by: wangkx <kevin.wang@lexisnexis.com>