Add RedshiftSQLHook, RedshiftSQLOperator

[Brooke-white]

closes: #16355 #16544

Adds RedshiftSQLHook and RedshiftSQLOperator, which allow Airflow users to execute Redshift operations.

RedshiftSQLHook is supported by the redshift_connector database driver which supports authenticating via IAM or Identity Provider. Integration with sqlalchemy is supported via sqlalchemy-redshift.

Unit tests have been added to:

• Test Hook -- ensuring connection parameters flow through to redshift_connector as expected
• Test Operator -- ensuring statements flow through to redshift_connector.execute method as expected

Docs have been added to:

• explain how to build a connection
• provide an example DAG with create/insert/select statements
• provide reference to redshift_connector docs for details about supported connection options

Use case / motivation

There is now a redshift_connector library which we can use instead of psycopg2. The redshift connector library provides support for IAM & Identity provider authentication as well as Redshift specific datatype support (e.g. GEOMETRY, SUPER, etc.).

See #16355 for more info.

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[boring-cyborg]

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[dstandish]

small things... looking good though 👍

One bigger thing is ... should we take this opportunity to replace the existing RedshiftHook (which is about managing clusters) with the one added in this PR (since this by far the more useful and needed one, and more deserving of the name RedshiftHook)

[ashb]

We don't need a whole new hook for this -- the existing Postgres hook will already connect to Redshift

https://airflow.apache.org/docs/apache-airflow-providers-postgres/stable/_api/airflow/providers/postgres/hooks/postgres/index.html#airflow.providers.postgres.hooks.postgres.PostgresHook

_If we decide we do want a hook for this anyway then it should probably subclass that postgres hook.

[ashb]

as well as Redshift specific datatype support (e.g. GEOMETRY, SUPER, etc.).

Geometry and Super are returned as strings -- isn't that the default behaviour for pscopg already?

[Brooke-white]

@ashb, PostgresHook does not support authenticating via identity provider. That functionality is a big part of #16355.

IMO It would make more sense to have a separate hook for Redshift as it's a different product than Postgres. PostgresHook is using a driver designed for Postgres. RedshiftSQLHook would use a driver designed for Redshift.

Geometry and Super are returned as strings -- isn't that the default behaviour for pscopg already?

Geometry can also be hex encoded under OID 3999, and requires manipulation by the driver before being returned to the user.

[Brooke-white]

Some info on authenticating via identity provider using redshift_connector 1 2

The datatypes redshift_connector supports 3

[boring-cyborg]

Awesome work, congrats on your first merged pull request!