Hello, I'm working with AWS redshift database. I'm using Ecto.Adapters.SQL.Sandbox in tests and problem with it is that when error occurs in DB adapter tries to rollback to savepoint. The thing is that redshift database doesn't support savepoints – so DB returns error that it doesn't support savepoints and initial error is hidden. Maybe we should allow to specify for repo config that DB doesn't supports savepoints ?
How to reproduce:
1. Create any table with not nullable column in Redshift
2. Setup Ecto.Adapters.SQL.Sandbox for redshift test
3. In test try to use `Repo.insert_all` where struct has not nullable column set to nil.
DB will return error that savepoints not supported:
(Postgrex.Error) ERROR 0A000 (feature_not_supported) SQL command "ROLLBACK TO SAVEPOINT postgrex_query" not supported
To look at actual error you need to modify test to run unboxed.