Fix timezone handling when creating documentations

aleksis/apps/alsijil/schema/documentation.py

-from datetime import datetime
+from datetime import datetime, timezone
 import graphene
 from graphene_django.types import DjangoObjectType
 from graphene_django_cud.mutations import (
@@ -149,16 +149,18 @@ class DocumentationBatchCreateOrUpdateMutation(graphene.Mutation):
             ):
                 raise PermissionDenied()
 
+            # Timezone removal is necessary due to ISO style offsets are no valid timezones. Instead, we take the timezone from the lesson_event and save it in a dedicated field.
             return Documentation.objects.create(
-                datetime_start=datetime.fromisoformat(datetime_start),
-                datetime_end=datetime.fromisoformat(datetime_end),
+                datetime_start=datetime.fromisoformat(datetime_start).replace(tzinfo=timezone.utc),
+                datetime_end=datetime.fromisoformat(datetime_end).replace(tzinfo=timezone.utc),
+                timezone=lesson_event.timezone,
                 lesson_event=lesson_event,
                 course=lesson_event.course,
                 subject=lesson_event.subject,
                 topic=doc.topic or "",
                 homework=doc.homework or "",
                 group_note=doc.group_note or "",
-            )  # TODO: Add course & subject
+            )
         else:
             obj = Documentation.objects.get(id=id)