Add --export-from to allow for generating incremental data

[serramatutu]

This commit adds an --export-from flag which allows generating incremental data. This is useful for generating data every day instead of having to export the CSV of all years at once.

[sharisiri]

Edit: Just saw the cache-state branch. Excited to play with those new features when they're ready.

Hi @serramatutu, thanks for a great feature.

I am playing around with the new flag but unable to generate daily data.

For instance jafgen --export-from '2018-09-01' and jafgen 2 --export-from '2018-09-01' work fine but they generate at least a years worth of data.

jafgen --export-from '2024-05-15' results in UserWarning: start_from is after end of simulation. All data will be empty except for slowly changing dimensions.

Can you please elaborate on how to generate orders for one day preferably from the current date?

Thanks!