Pluggable invoice transmission methods (#5020)

* Flexible invoice transmission

* UI work

* Add peppol and output

* API support

* Profile integration

* Simplify form for individuals

* Remove sent_to_customer usage

* more steps

* Revert "Bank transfer: Allow to send the invoice direclty to the accounting department (#2975)"

This reverts commit cea6c340be.

* minor fixes

* Fixes after rebase

* update stati

* Backend view

* Transmit and show status

* status, retransmission

* API retransmission

* More fields

* API docs

* Plugin docs

* Update migration

* Add missing license headers

* Remove dead code, fix current tests

* Run isort

* Update regex

* Rebase migration

* Fix migration

* Add tests, fix bugs

* Rebase migration

* Apply suggestion from @luelista

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

* Apply suggestion from @luelista

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

* Apply suggestion from @luelista

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

* Apply suggestion from @luelista

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

* Apply suggestion from @luelista

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

* Make migration reversible

* Add TransmissionType.enforce_transmission

* Fix registries API usage after rebase

* Remove code I forgot to delete

* Update transmission status display depending on type

* Add testmode_supported

* Update src/pretix/static/pretixbase/js/addressform.js

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

* Update src/pretix/static/pretixbase/js/addressform.js

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

* Update src/pretix/static/pretixbase/js/addressform.js

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

* New mechanism for non-required invoice forms

* Update src/pretix/base/invoicing/transmission.py

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

* Declare testmode_supported for email

* Make transmission_email_other an implementation detail

* Fix failing tests and add new ones

* Update src/pretix/base/services/invoices.py

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

* Add emails to email history

* Fix comma error

* More generic default email text

* Cleanup

* Remove "email invoices" button and refine logic

* Rebase migration

* Fix edge case

---------

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

src/tests/testdummy/signals.py

@@ -22,6 +22,10 @@
 from django.dispatch import receiver
 
 from pretix.base.channels import SalesChannelType
+from pretix.base.invoicing.transmission import (
+    TransmissionProvider, transmission_providers,
+)
+from pretix.base.models import Invoice
 from pretix.base.signals import (
     register_payment_providers, register_sales_channel_types,
     register_ticket_outputs,
@@ -70,3 +74,37 @@ def html_head_presale(sender, request=None, **kwargs):
         # No tracking scripts on PCI DSS relevant payment pages
         return ""
     return "<script>alert('BAD TRACKING SCRIPT')</script>"
+
+
+@transmission_providers.new()
+class TestSdiTransmissionProvider(TransmissionProvider):
+    identifier = "fatturapa_test"
+    type = "it_sdi"
+    verbose_name = "FatturaPA Test"
+
+    def is_ready(self, event) -> bool:
+        return True
+
+    def is_available(self, event, country, is_business: bool) -> bool:
+        return str(country) == "IT"
+
+    def transmit(self, invoice):
+        invoice.transmission_status = Invoice.TRANSMISSION_STATUS_COMPLETED
+        invoice.save()
+
+
+@transmission_providers.new()
+class TestPeppolTransmissionProvider(TransmissionProvider):
+    identifier = "peppol_test"
+    type = "peppol"
+    verbose_name = "PEPPOL Test"
+
+    def is_ready(self, event) -> bool:
+        return True
+
+    def is_available(self, event, country, is_business: bool) -> bool:
+        return is_business
+
+    def transmit(self, invoice):
+        invoice.transmission_status = Invoice.TRANSMISSION_STATUS_COMPLETED
+        invoice.save()