HPCC-12213 Add new WsDFU method to retrieve meta data

A new WsDFU method DFUGetFileMetaData is added to
retrieve MetaData from DFU IResultSetMetaData.

Signed-off-by: wangkx <kevin.wang@lexisnexis.com>
Is this code just here for error checking?  If so it is worth commenting.  Is it worth the dali lookup?