[ADAP-610] [Spike] Investigate if region is absolutely required

[dbeatty10]

Question to answer

• Is passing a region to redshift_connector absolutely necessary? i.e., must it be a breaking change in dbt-redshift 1.5?

Context

1. The region was hard-coded to be parsed from the hostname when switching from psycopg2 to redshift_connector in Modify RedshiftConnectionManager to extend from SQLConnectionManager, migrate from psycopg2 to redshift python connector #251.
2. An optional region config for dbt-redshift profiles was added in Fix for #419: dbt-redshift 1.5 does not work with non-standard redshift hostnames #420, but it still tries to infer the region from the host name when it is not provided.

See #419 for situations where the region can't be inferred from the host.

The redshift_connector docs have region listed as optional, so maybe there are scenarios in which we can omit supplying it.

Feedback

#419 (comment)

Looking into this, it seems like region isn't a required parameter at all at least if you are connecting with a username and password. Can we investigate if we can either not require region at all or only require it in situations where it is actually required?

See #483 for an additional request to make this non-breaking in 1.5.