[14.0] [IMP] l10n_it_delivery_note: prevent invoice creation

[renda-dev]

In some cases, the possibility to create an invoice for a single DN could be misleading.

• Added "Do not allow single DN invoicing" checkbox in the delivery note type
• Make invoice button invisible if that setting is enabled

[OCA-git-bot]

Hi @MarcoCalcagni, @aleuffre, some modules you are maintaining are being modified, check this out!