Handle JSON & new columns in Airtable `fare_systems` in dbt

[lauriemerrell]

As far as I know, no one is using fare systems data in the warehouse at time of writing (November 2023). This ticket will only become relevant if that changes.

As a data user who needs to access Airtable fare systems data in the data warehouse, I need the schemas for that data to be updated in dbt so that I can use new and changed fields in the warehouse

PR #3067 changed some columns to JSON type and added new columns to the external table for fare systems that haven't been added to dbt yet. If we want these columns to be available and usable in the data warehouse, we will need to make dbt-side updates to handle these columns (unpack/cast JSON and add the new columns).

Here's a summary of the changes in the external table, which will need to be handled on the dbt side if anyone wants access to this data in the warehouse:

column_name	change_type	change_details
distance_fares	new_column
fare_account	new_column
fare_capping	type_change	STRING to JSON
fare_media	new_column
fare_product_price_max	new_column
fare_product_price_min	new_column
fare_products	new_column
fare_products_notes	new_column
free_fare	new_column
interagency_xfer_discounts	new_column
interagency_xfer_notes	new_column
interagency_xfer_systems	new_column
intra_system_xfer_cost	new_column
intra_system_xfer_discounts	new_column
intra_system_xfer_time	new_column
market_based_fares	new_column
num_reduced_fare_categories	new_column
payment_accepted	type_change	STRING to JSON
reduced_fare_categories	type_change	STRING to JSON
route_fares	new_column
smartcard_discount	new_column
ticket_media	type_change	STRING to JSON
ticket_pass_sales_methods	type_change	STRING to JSON
ticket_validation	type_change	STRING to JSON
youth_specific_fare	new_column
zone_fares	new_column