HPCC-9742 Allow maxlength to be specified on workunit output

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Merge pull request #5290 from ghalliday/issue9742

HPCC-9742 Allow maxlength to be specified on workunit output

Reviewed-By: Jamie Noss <james.noss@lexisnexis.com>
Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>