HPCC-10674 ECL support for writing JSON files

Signed-off-by: Anthony Fishbeck <anthony.fishbeck@lexisnexis.com>
HPCC-10674 Update based on review

Signed-off-by: Anthony Fishbeck <anthony.fishbeck@lexisnexis.com>
HPCC-10674 Update based on review

Signed-off-by: Anthony Fishbeck <anthony.fishbeck@lexisnexis.com>
Merge pull request #6421 from afishbeck/jsonWriteFilesEx

HPCC-10674 ECL support for writing JSON files

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>