Send invoice to Holded

Ensures an invoice exists in Holded: uses its link, adopts the one carrying its marker, or creates it with the contact and taxes from the connection. A validated invoice arrives with the Filmo number, and Filmo advances the counter of the billing line for its series so Holded does not reuse it. A draft arrives as a Holded draft through the billing line for its series, with the total calculated by Holded (checked on approval). Validating and sending it again replaces it with the final invoice and its number, or approves it in place if it already had that number.