This update adds a reusable helper for retrieving default sale order IDs, making it easier for customizations to adapt sales behavior without duplicating logic. It is mainly an internal improvement that supports cleaner extensions and future maintenance.

in this commit:
- added a  helper function to get sale order ids which can be override in
  inherited models.

---
I confirm I have signed the CLA and read the PR guidelines at www.odoo.com/submit-pr