Invoices: Allow issuing invoices only to businesses (Z#23220397) (#5807)

* Invoices: Allow issuing invoices only to businesses

In situations where every invoice has a significant accounting cost and
consumers usually do not need invoices, this can save a lot of money or
effort.

* Improve backend UI if not qualified for invoice

src/pretix/base/settings.py

@@ -1225,6 +1225,15 @@ DEFAULTS = {
         'default': json.dumps(['web']),
         'type': list
     },
+    'invoice_generate_only_business': {
+        'default': 'False',
+        'type': bool,
+        'form_class': forms.BooleanField,
+        'serializer_class': serializers.BooleanField,
+        'form_kwargs': dict(
+            label=_("Only issue invoices to business customers"),
+        )
+    },
     'invoice_address_from': {
         'default': '',
         'type': str,