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>
In this method, we do not need to set the ColumnSize which is the length of the ColumnLabel.