After ITPART-1238, the IT Partner Gateway team consulted the Subscription and Product Team who discouraged the usage of the Subscription ID because it's an internal database key they don't want to expose.

Instead we should always use the subscription number.

I've confirmed that we don't have duplicated subscription with the same subscription_number and start_date values.
Also, I've checked that all the messages we receive from the canonical gateway and IT partner gateway contain the subscription number.

This would mean to:

• Change the primary key for the subscriptions table from subscription id, start date to subscription number and start data.
• Change some APIs to expose the subscription number instead of the subscription ID
• Stop calling the Subscription API to populate the subscription ID: