Write to `.parquet` files: Partition patterns other than date parts?

[flarco]

Discussed in #605

^{Originally posted by fdcastel July 15, 2025}
According to the docs:

You must specified the update_key along with a part_ variable in the object_name, for example: object: my/folder/{part_year_month}/{part_day}.

What if I want to partition by some other column in my dataset (e.g. product_type)?