Explicitly store whether checkins were offline (#2617)

src/pretix/base/migrations/0216_checkin_forced_sent.py

@@ -0,0 +1,18 @@
+# Generated by Django 3.2.12 on 2022-04-29 13:56
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('pretixbase', '0215_customer_organizer_identifier_unique'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='checkin',
+            name='force_sent',
+            field=models.BooleanField(default=False, null=True),
+        ),
+    ]