add ALTER TABLE support for duckdb (motherduck) tables

[wuputah]

Description

Currently, you can't use ALTER TABLE to modify a table that uses the duckdb access method:

postgres=# ALTER TABLE a RENAME TO b;
ERROR:  DuckDB does not support ALTER TABLE yet

The basics to consider:

• ALTER TABLE RENAME support #537
• ALTER TABLE ADD COLUMN support #538
• ALTER TABLE RENAME COLUMN support #539
• ALTER TABLE DROP COLUMN support #540
• ALTER TABLE ALTER COLUMN TYPE support #541

[JelteF]

Thanks for creating this. I used it as a reason to try out GitHubs new sub-issue feature