HPCC-9286 Allow multiple optional atmost conditions.

Also fixes:

HPCC-9711 Ensure only the atmost condition is used for calculating the hard matches.
HPCC-10005 Global ATMOST prefix join in thor may lose results

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Merge pull request #4817 from ghalliday/issue9711

HPCC-9286 Allow multiple optional atmost conditions.

Reviewed-By: Jamie Noss <james.noss@lexisnexis.com>
Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>