adopted flex files:

• locations.geojson (will also involve standardizing tlib's support for geojson)
• location_groups.txt
• location_group_stops.txt
• booking_rules.txt

flex extensions desired by @tsherlockcraig:

• stop_times.txt mean_duration_factor
• stop_times.txt safe_duration_factor
• https://github.com/MobilityData/gtfs-flex/blob/dda6ba0982236d81867fbad5163c7a59689830d1/spec/reference.md?plain=1#L94-L95

Note that we want to ensure that we're collecting routes.txt continuous_pickup and continuous_drop_off but will not be using it in this sprint