feat: add sourceColumnMatch support for External Tables

[google-labs-jules]

Add sourceColumnMatch option to IExternalDataConfiguration in src/types.d.ts to support matching loaded columns to the schema by name or position for external tables. This mirrors recent API updates.

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PR created automatically by Jules for task 574555129115614399 started by @danieljbruce

[google-labs-jules]

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[alvarowolfx]

this is handled by the discovery automation #1550, we just need to make sure this gets merged