HPCC-8661 Add support for DICTIONARYs in the payload of a key

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
Merge pull request #3997 from richardkchapman/dict-index

HPCC-8661 Add support for DICTIONARYs in the payload of a key

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>