[issue#14490][IMP] invoice_xunnel: Included new field that saves the amount difference allowed between the amount in the XML and the invoice.

[IMP] invoice_xunnel: Included new field that saves the amount difference allowed between the amount in the XML and the invoice.

This is already implemented in vendor-bills.

Functional test before fix https://youtu.be/lUSpoQ4_LrQ

Functional test after fix https://youtu.be/XWOqqvRq-co

[REF] invoice_xunnel: complete search_invoice method to align it to vendor-bills

https://git.vauxoo.com/vauxoo/vendor-bills/-/merge_requests/153

Functional test before fix https://youtu.be/XWOqqvRq-co

Functional test after fix https://youtu.be/xUBmiaUuoOc