Enable DuckDB Extensions for connector

[archiewood]

See #644

HTTPFS is allows you to query CSV / parquet files that are stored in S3 using DuckDB

Implementation ideas

• Checkbox in the settings UI where you connect to DuckDB ("Use HTTPFS" or similar), which then shows fields to enter of s3_region and s3_access_key_id, and s3_secret_key_id.
• Use the duckdb connector to conditionally run the required SQL statements, if HTTPFS is selected?

[archiewood]

It would also be good to enable https://duckdb.org/docs/guides/import/excel_import.html for users.

[hydrojumbo]

JSON support would make it easier to handle JSON columns in queries: https://duckdb.org/docs/extensions/json.html#installing-and-loading. For now, this can be handled in the sources query if the source database supports it.

[archiewood]

Support for DuckDB extension autoloading shipped with DuckDB 1.0, so any of the default library of extensions should work in DuckDB source queries.

Other extension not yet supported