Test different incremental load strategies supported by dbt-duckdb

[chrisgebert]

From https://github.com/duckdb/dbt-duckdb:

dbt-duckdb supports the delete+insert and append strategies for incremental table models, but unfortunately it does not yet support incremental materialization strategies for external models.

[chrisgebert]

delete + insert seems to be the choice to overwrite existing records that have been updated since a previous snapshot file. I'll need to confirm the columns that should be included/excluded.