HPCC-10617 Add support for Cassandra

Initial checkin of plugin to support embedding of Cassandra (CQL) queries.

Because the Cassandra cpp library does not provide information about the
expected types for bound parameters, and yet is very fussy that they match
whcat it wanted, this required a change to the embed API to allow the
information to be taken from the ECL parameter types.

Note that the Cassandra cpp interface libraries are currently only available
in source form (and building them relies on other libraries that are not
available on most distros), so the build process will require some work and/or
documentation.

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>
embed is really the invers of import, at least at present. But I guess it's more future-proof. I'll add a bit.