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>
I agree. The IDFUFileMetaDataReader can be added later if it is needed. I will remove it now.