New data model for default tax rule and new options for cancellation fees (#4962)

* New data model for default tax rule

* Remove misleading empty label when field is not optional

* Allow to split cancellation fee

* Fix API and tests

* Update migration

* Update src/tests/api/test_taxrules.py

Co-authored-by: luelista <weller@rami.io>

* Update src/tests/api/test_taxrules.py

Co-authored-by: luelista <weller@rami.io>

* Review note

* Update src/pretix/base/models/tax.py

Co-authored-by: luelista <weller@rami.io>

* Flip API behaviour for default

* Fix failing tests

* Fix failing test

* Split migration

---------

Co-authored-by: luelista <weller@rami.io>

src/pretix/control/forms/event.py

@@ -761,6 +761,7 @@ class CancelSettingsForm(SettingsForm):
         'change_allow_user_addons',
         'change_allow_user_if_checked_in',
         'change_allow_attendee',
+        'tax_rule_cancellation',
     ]
 
     def __init__(self, *args, **kwargs):
@@ -783,14 +784,8 @@ class PaymentSettingsForm(EventSettingsValidationMixin, SettingsForm):
         'payment_term_accept_late',
         'payment_pending_hidden',
         'payment_explanation',
+        'tax_rule_payment',
     ]
-    tax_rate_default = forms.ModelChoiceField(
-        queryset=TaxRule.objects.none(),
-        label=_('Tax rule for payment fees'),
-        required=False,
-        help_text=_("The tax rule that applies for additional fees you configured for single payment methods. This "
-                    "will set the tax rate and reverse charge rules, other settings of the tax rule are ignored.")
-    )
 
     def clean_payment_term_days(self):
         value = self.cleaned_data.get('payment_term_days')
@@ -804,10 +799,6 @@ class PaymentSettingsForm(EventSettingsValidationMixin, SettingsForm):
             raise ValidationError(_("This field is required."))
         return value
 
-    def __init__(self, *args, **kwargs):
-        super().__init__(*args, **kwargs)
-        self.fields['tax_rate_default'].queryset = self.obj.tax_rules.all()
-
 
 class ProviderForm(SettingsForm):
     """