Expose DuckDB COPY Command to Postgres

[philippemnoel]

What feature are you requesting?

An easy way to load data between DuckDB and external files is via the COPY command. We should expose it, as it is especially difficult to load data into Postgres that's in format like Parquet aside from via the FDW.

Why are you requesting this feature?

See above^

What is your proposed implementation for this feature?

See here: https://duckdb.org/docs/sql/statements/copy.html for reference. Expose the command in a similar fashion to how we expose other DuckDB commands.

Full Name:

Philippe Noël

Affiliation:

ParadeDB

[rebasedming]

Duplicate of #107