Allow payment providers to define custom form fields / templates

src/pretix/plugins/banktransfer/payment.py

@@ -1,4 +1,6 @@
 from collections import OrderedDict
+from django.template import Context
+from django.template.loader import get_template
 from django.utils.translation import ugettext_lazy as _
 from django import forms
 
@@ -16,3 +18,8 @@ class BankTransfer(BasePaymentProvider):
              required=False
          ))
     ])
+
+    def checkout_form_render(self, request) -> str:
+        template = get_template('pretixplugins/banktransfer/checkout_payment_form.html')
+        ctx = Context({'request': request, 'event': self.event, 'settings': self.settings})
+        return template.render(ctx)