Expand ftw download command to get source data

[cholmes]

The source geoparquet polygons are all at locations like https://beta.source.coop/repositories/kerner-lab/fields-of-the-world-austria/

It'd be great to have the ftw download command enable users to easily pull those down as well.

[cholmes]

The structure of the command should be the same - let people select the country and just get that, so I lean towards putting it in the same command - like ftw download --fiboa-only, but we could have ftw download fiboa or something, like a separate command with the same semantics.