confirmation: Migrate Confirmation to bigint.

This model has no external references, and is among the larger
tables.  Migrate it to bigint.

confirmation/migrations/0012_alter_confirmation_id.py

@@ -0,0 +1,17 @@
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("confirmation", "0011_alter_confirmation_expiry_date"),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name="confirmation",
+            name="id",
+            field=models.BigAutoField(
+                auto_created=True, primary_key=True, serialize=False, verbose_name="ID"
+            ),
+        ),
+    ]