Rename label sales_order_id to sales_order for consistency and clarity

[HappyTetrahedron]

Summary

• The label used for deriving the correct Sales Order is now expected as sales_order instead of sales_order_id (since the label value does not actually correspond to the ID of the sales order in Odoo, but to the name). This breaks existing queries which provide the old sales_order_id label.

Checklist

• Categorize the PR by setting a good title and adding one of the labels:
  bug, enhancement, documentation, change, breaking, dependency
  as they show up in the changelog
• Update tests.

[HappyTetrahedron]

We don't have existing queries, so this is the moment to fix the inconsistency, else it'll be too late.

[Kidswiss]

🍾