Redshift specific dialect and/or multi-row insert

We've been using this JDBC connector against Redshift and have run into a number of shortcomings.

Specifically there are 2 main issues, the first is the `string` -> `TEXT` -> `VARCHAR(256)` mapping (which essentially renders the `auto.create` functionality useless) and the second is the incredibly slow writes resulting from inserts records one at a time in Redshift.

I put together a rough spike here to test out some potential improvements and the results are promising. You can find my PR here:
https://github.com/meroxa/aiven-kafka-connect-jdbc/pull/1

I'd love to collaborate on getting this work done and shipped if there's interest.