Add Redshift External Table support

[alondhe]

Is your feature request related to a problem? Please describe.
Redshift external tables cannot be used in WhiteRabbit today, as the step of retrieving table names is based upon using the information_schema: https://github.com/OHDSI/WhiteRabbit/blob/master/rabbit-core/src/main/java/org/ohdsi/databases/RichConnection.java#L160

Describe the solution you'd like
I believe we could add support by having a Redshift specific route that looks at regular and external tables. Something like:

SELECT table_name FROM information_schema.tables WHERE table_schema = 'y202212' union SELECT tablename FROM SVV_EXTERNAL_TABLES where schemaname = 'y202212';

Another approach could be to use the same method as DatabaseConnector, which uses the getTables() java function; this has recently been enhanced by @schuemie to allow for EXTERNAL TABLES: OHDSI/DatabaseConnector#210.

Describe alternatives you've considered
We're going to create regular tables off of the external tables for now.

Tagging my colleague @rfherrerac