🧑‍💻(backend) complete no payment order

[jbpenrath]

Purpose

Some state source were missing for complete and pending_payment transition. We fix that. Furthermore, we recently create a failed installment payment order but we forgot to link an invoice to this order, so it leads to issues when trying to use this order for development.

Proposal

Description...

• [x] Update order flow to add missing source transition
• [x] Update demo_dev script to work as expected