[IMP] account: vendor bill creation upon email reception

This allows to set up a mail alias per purchase journal. Then share that email address to your supplier, or use it internally to forward the vendor bills received by mail, to automatically create an empty vendor bill with the mail attachments linked, and the partner might be filled if the source email matches a supplier.

Thanks to the document preview on the side, it's now super easy and super fast to copy the vendor bill info from the received PDF into the account.invoice object. This would eventually be improved later on (IAP).

Was task: 37703
Was PR #22158