Description

Postgres does not support a type similar to the DuckDB UNION type. So we need to make some concessions here. What we can do is the following:

1. If people actually select a UNION column in the output of their query, we should probably just convert it to its text representation.
2. We should add a duckdb.union type, for which we implement the union_extract and union_tag functions, so people can extract duckdb.unresolved_type values from it.

Once we do this we can un-exclude: