Recover abandoned carts

[dawn-stripe]

Add a recovery flow for abandoned carts, i.e. Checkout sessions that expire before the customer completes their purchase. This flow has a few pieces:

• Collect consent from the customer to receive promotional emails: Within our Checkout Session create call, we need to configure Checkout to collect consent
• Configure recovery options: Within our Checkout session create call we'll add the after_expiration configuration options so that Checkout will generate a recovery URL we can send to customers. We'll also add support for promotional codes to that session so that we can use a discount to incentive our customers to complete their purchase
• Listen for checkout.session.expired events: when we receive one of these we'll look at whether we have consent from the customer to email them and if so, we'll send them an email with the recovery url from the session.
• Other enhancements: We reduced our expiration time on the session so we know earlier on that the customer has abandoned their cart. We also started tracking the recoved_from attribute on the session when we get a checkout.session.completed event, this can help us track conversion from our email outreach.