[18.0][MIG] account_payment_term_partner_holiday: Migration to 18.0

[MPoch-PlanetaTIC]

I will migrate account_payment_term_partner_holiday module from 16.0 to 18.0

[MPoch-PlanetaTIC]

PR pushed: #951
The new feature is: the due date is set according to the partner's vacation when confirming an invoice with a set payment term.