This update adds three new fields to invoices generated for Chorus Pro compliance – Buyer Reference, Contract Reference, and Purchase Order Reference. These fields appear in the invoice header, allowing for accurate documentation required by Chorus Pro and improving data tracking for financial reporting.

This commit:
- Add three reference fields to invoice PDF for Chorus Pro compliance: Buyer Reference, Contract Reference, and Purchase Order Reference. These fields appear in the invoice header when set on the invoice.

task-5410836

Forward-Port-Of: odoo/odoo#240494