Add data migration

aleksis/apps/paweljong/migrations/0024_add_cost_to_registration.py

+# Generated by Django 3.2.19 on 2023-06-04 14:54
+
+from django.db import migrations, models
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('paweljong', '0023_eventregistration_cost'),
+    ]
+
+    operations = [
+        migrations.RunSQL("UPDATE paweljong_eventregistration SET cost = (SELECT paweljong_event.cost FROM paweljong_event WHERE paweljong_event.id = paweljong_eventregistration.event_id);")
+    ]