Automatically output files for DuckDB

### Feature description

- following to #267

COPY TO '{{ outputFiles.result }}' — if you have any files generated within the query that weren’t in the wdir before the task run, we can automatically output them without requiring to specify any outputFiles objects. This syntax will still work if specified, but it's no longer required. we can deprecate the outputFiles property because it will now be done by default (TBD if possible)

Start by reading the related issue #267 and reviewing how DuckDB COPY TO and the outputFiles property are currently handled. Determine whether files generated during a query can be detected and output automatically, while preserving the existing syntax or defining its deprecation. Done means the behavior is specified and implemented without requiring outputFiles objects.

Written by the indexing model from the issue text.