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 would be inclined for this to be in fileview.hpp or similar so that it is close to the definition of the enumeration - so that if that gets updated this also stands more chance of being kept in sync.