HPCC-11060 - Support multi-qualifiers on sds subscription nodes

e.g. support querySDS().subscribe("/a/b[@a1='v1][@a2='v2']");

Signed-off-by: Jake Smith <jake.smith@lexisnexis.com>
HPCC-11060 - Changes following review

Signed-off-by: Jake Smith <jsmith@lexisnexis.com>
HPCC-11060 - Minor changes following review

Signed-off-by: Jake Smith <jake.smith@lexisnexis.com>
Merge pull request #5565 from jakesmith/hpcc-11060

HPCC-11060 - Support multi-qualifiers on sds subscription nodes

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>