AppConfigs set default_auto_field

Django used to default this, but it generates a warning now.

kepi/sombrero_sendpub/apps.py

@@ -0,0 +1,5 @@
+import django.apps
+
+class SombreroApiConfig(django.apps.AppConfig):
+    name = 'kepi.sombrero_sendpub'
+    default_auto_field = 'django.db.models.AutoField'

kepi/trilby_api/apps.py

@@ -1,5 +1,5 @@
-from django.apps import AppConfig
+import django.apps
 
-
-class TrilbyApiConfig(AppConfig):
+class TrilbyApiConfig(django.apps.AppConfig):
     name = 'kepi.trilby_api'
+    default_auto_field = 'django.db.models.AutoField'