feat(resource_redshift_database): basic zeroetl support

[Intuinewin]

SmallPR which enables zeroetl support for the database resource

Unfortunately, I haven't found a way to query on the cluster if a db is associated with an integration

Ref: https://docs.aws.amazon.com/redshift/latest/dg/r_CREATE_DATABASE.html

[mmichaelb]

Thank you for your contribution. Again, sorry for the late feedback. The PR looks good so far but an integration/acceptance test is missing. Please provide one simple parameterized test that can be used to test a zeroetl database integration.

[alexjurkiewicz]

I asked Claude to address the review feedback because this feature is also potentially useful to us. Here are the commits we came up with:

• 849ec78 — Replace ExactlyOneOf with ConflictsWith on datashare_source and zeroetl_integration. ExactlyOneOf requires one of the two to always be set, which prevents creating a plain local database. ConflictsWith allows both to be absent while still preventing them from being combined.

• 12844ad — Preserve zeroetl_integration state across Read. The Redshift catalog doesn't expose the integration ID after creation, so Read can't reconstruct it. Without this fix, subsequent plans show spurious drift and destroy/recreate the database.

• a13e588 — Acceptance test for the conflict validation (TestAccResourceRedshiftDatabase_ZeroETLConflictsWithDatashare). This runs without any special infrastructure — it only needs a Redshift connection.

• 5e3ed36 — Acceptance test for the full zero ETL flow (TestAccResourceRedshiftDatabase_ZeroETL). Skipped unless REDSHIFT_ZERO_ETL_INTEGRATION_ID is set. Requires a pre-existing zero ETL integration and a cluster of ra3.xlplus or larger.

[Intuinewin]

Thanks @alexjurkiewicz , I cherry-picked your commits except 12844ad as I don't think it's necessary