HPCC-12161 Cassandra plugin should distinguish ASCII from TEXT fields

Note - also corrects incorrect key file that was causing false positives from
overnight build and test.

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
Merge pull request #6504 from richardkchapman/cassandra-ascii

HPCC-12161 Cassandra plugin should distinguish ASCII from TEXT fields

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>