HPCC-12390 Allow variable parameters to SAMPLE

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
HPCC-12390 Move and update the test case

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Merge pull request #6538 from ghalliday/issue12390

HPCC-12390 Allow variable parameters to SAMPLE

Reviewed-By: Jamie Noss <james.noss@lexisnexis.com>
Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>