SaleTunnel v2 - pending -> pending_payment transition

[jbpenrath]

Bug Report

Problematic behavior
Currently, an order in pending state can transition to pending_payment once we try to update its state.

Expected behavior/code
An order should be able to transition from pending to pending_payment only if the first installment has been paid and all other installments are not refused.

Steps to Reproduce

1. Create an order with a state to pending
2. Call order.flow.update()
3. The order state has been updated to pending_payment

Environment

• Joanie version: dev