Add note field and external identifier to customers (#2605)

src/pretix/base/migrations/0214_customer_notes_ext_id.py

@@ -0,0 +1,23 @@
+# Generated by Django 3.2.12 on 2022-04-28 08:37
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('pretixbase', '0213_discount_condition_ignore_voucher_discounted'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='customer',
+            name='external_identifier',
+            field=models.CharField(max_length=255, null=True),
+        ),
+        migrations.AddField(
+            model_name='customer',
+            name='notes',
+            field=models.TextField(null=True),
+        ),
+    ]