BankTransfer: Generate invoice after payment if invoice_generate=paid (Z#23144775)

[pc-coholic]

As of right now, the invoice-generation for Bank Transfer did not work as expected: the requires_invoice_immediately caused the invoice to be generated before the payment, thus generating an invoice without the Mollie payment information.

This change:

• Defaults the requires_invoice_immediately property back to False (since we do not want the invoice before the payment)
• Adds handling for invoice-generation after the payment if invoice_generate is set to paid if requires_invoice_immediately is True.