HPCC-11310 Fix signature of addNamedQuery() in workunit.hpp

Snapshot parameter was added to the method in the cpp but not
the header. Only used externally by eclserver.

Signed-off-by: Anthony Fishbeck <anthony.fishbeck@lexisnexis.com>
Merge pull request #5772 from afishbeck/lnnamedquery

HPCC-11310 Fix signature of addNamedQuery() in workunit.hpp

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>