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/pretix/control/views/event.py

@@ -37,7 +37,7 @@ import json
 import logging
 import operator
 import re
-from collections import OrderedDict
+from collections import OrderedDict, defaultdict
 from decimal import Decimal
 from io import BytesIO
 from itertools import groupby
@@ -76,6 +76,9 @@ from i18nfield.utils import I18nJSONEncoder
 
 from pretix.base.email import get_available_placeholders
 from pretix.base.forms import PlaceholderValidator
+from pretix.base.invoicing.transmission import (
+    get_transmission_types, transmission_providers,
+)
 from pretix.base.models import Event, LogEntry, Order, TaxRule, Voucher
 from pretix.base.models.event import EventMetaValue
 from pretix.base.services import tickets
@@ -651,6 +654,22 @@ class InvoiceSettings(EventSettingsViewMixin, EventSettingsFormView):
     template_name = 'pretixcontrol/event/invoicing.html'
     permission = 'can_change_event_settings'
 
+    def get_context_data(self, **kwargs):
+        types = get_transmission_types()
+        providers = defaultdict(list)
+        ready = defaultdict(lambda: False)
+        for p, __ in transmission_providers.filter(active_in=self.request.event):
+            is_ready_result = p.is_ready(self.request.event)
+            providers[p.type].append((p, is_ready_result, p.settings_url(self.request.event)))
+            ready[p.type] = ready[p.type] or is_ready_result
+        for k, v in providers.items():
+            v.sort(key=lambda p: (-p[0].priority, p[0].identifier))
+        return super().get_context_data(
+            transmission_providers=providers,
+            transmission_types=types,
+            ready=ready,
+        )
+
     def get_success_url(self) -> str:
         if 'preview' in self.request.POST:
             return reverse('control:event.settings.invoice.preview', kwargs={