parse_subscription: get account_type from configuration file rather than WC subscription.

This MR modifies parse_subscription so it infers account_type and billing_period of a subscription by checking what is configured in upgrades_downgrades.yml file.

Before this was done looking at the json data on the WC subscriptions. This failed in some instances and worked on others because of the different names that different WC instances were giving to the bundles.