* move set_allowed_event_props into context module

* extract parse_csv fn

* add custom_props.csv to CSV export (under FF)

* add test for custom prop export with a prop filter

* add test for goal filtered scenario

* mix format

* fix flaky test

* extract breakdown_custom_prop_values function

* Revert "fix flaky test"

This reverts commit 256b9bb2e71464ddf711d0cd7d537c2068d38a6c. The flaky
test was already fixed in https://github.com/plausible/analytics/pull/3184/commits/86557b18789e5087b59db722b7012be835ad7b7b

* make set_allowed_event_props a bang function

* test that all files are included in the CSV export