Optionally use BigQuery jobs API

### What feature or improvement would you like to see?

Per [this thread](https://github.com/dbt-labs/dbt-core/issues/13305#issuecomment-3175019702), BigQuery's API returns an error whenever the credential lacks `roles/bigquery.readSessionUser`.

I suggest we either:
- Try using the Read API and fall back to the regular REST API in case the user has `roles/bigquery.jobUser` but not `roles/bigquery.readSessionUser`
- Add a driver parameter like `adbc.bigquery.backend_api` which defaults to `read_api` but can also be set to `jobs_api` to allow users to set which API they want to use.