Add program times for items (Z#23178639)

* Add program times for items

* Fix frontend date validation

* Add ical data for program times [wip]

* Improve ical data for program times

* Remove duplicate code and add comments

* Adjust migration

* Remove program times form for event series

* Add pdf placeholder [wip]

* Improve explanation text with suggestion

Co-authored-by: Raphael Michel <michel@pretix.eu>

* Fix import sorting

* Improve ical generation

* Improve ical entry description

* Fix migration

* Add copyability for program times fot items and events

* Update migration

* Add API endpoints/functions, fix isort

* Improve variable name

Co-authored-by: Richard Schreiber <schreiber@rami.io>

* Remove todo comment

* Add documentation, Change endpoint name

* Change related name

* Remove unnecessary code block

* Add program times to item API

* Fix imports

* Add log text

* Use daterange helper

* Add and update API tests

* Add another API test

* Add program times to cloning tests

* Update query count because of program times query

* Invalidate cached tickets on program time changes

* Reduce invalidation calls

* Update migration after rebase

* Apply improvements to invalidation from review

Co-authored-by: Richard Schreiber <schreiber@rami.io>

* remove unneccessary attr=item param

* remove unnecessary kwargs for formset_factory

* fix local var name being overwritten in for-loop

* fix empty formset being saved

* Use subevent if available

* make code less verbose

* remove double event-label in ical desc

* fix unnecessary var re-assign

* fix ev vs p.subevent

---------

Co-authored-by: Raphael Michel <michel@pretix.eu>
Co-authored-by: Richard Schreiber <schreiber@rami.io>

src/pretix/control/views/pdf.py

@@ -44,7 +44,9 @@ from pypdf.errors import PdfReadError
 from reportlab.lib.units import mm
 
 from pretix.base.i18n import language
-from pretix.base.models import CachedFile, InvoiceAddress, OrderPosition
+from pretix.base.models import (
+    CachedFile, InvoiceAddress, ItemProgramTime, OrderPosition,
+)
 from pretix.base.pdf import get_images, get_variables
 from pretix.base.settings import PERSON_NAME_SCHEMES
 from pretix.control.permissions import EventPermissionRequiredMixin
@@ -95,6 +97,9 @@ class BaseEditorView(EventPermissionRequiredMixin, TemplateView):
                                                description=_("Sample product description"))
         item2 = self.request.event.items.create(name=_("Sample workshop"), default_price=Decimal('23.40'))
 
+        ItemProgramTime.objects.create(start=now(), end=now(), item=item)
+        ItemProgramTime.objects.create(start=now(), end=now(), item=item2)
+
         from pretix.base.models import Order
         order = self.request.event.orders.create(status=Order.STATUS_PENDING, datetime=now(),
                                                  email='sample@pretix.eu',