HPCC-9779 Add an internal option to generate the ecl for a subgraph

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Merge pull request #4708 from ghalliday/issue9779

HPCC-9779 Add an internal option to generate the ecl for a subgraph

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>