Sprint 6: Checkout

What's Changed

• docs: plan Sprint 6 checkout in the PRD and add payments setup by @romulojr-dev in #82
• feat: shipping data and fee rules by @romulojr-dev in #83
• feat: checkout steps, contact, delivery and review by @romulojr-dev in #84
• feat: place an order (#78) by @romulojr-dev in #85
• Pay with a Xendit payment session by @romulojr-dev in #86
• Payment webhooks (Xendit) by @romulojr-dev in #87
• docs: no network calls inside a transaction by @romulojr-dev in #89
• Auto-cancel unpaid orders and release stock by @romulojr-dev in #90
• startPayment: no Xendit calls inside the transaction by @romulojr-dev in #91

Full Changelog: v0.5.0...v0.6.0