Add public filters based on meta data (#3673)

* Add public filters based on meta data

* Fix licenseheaders

* ignore empty values

* Fix tests

* Full non-widget implementation

* Widget support

* Add a few tests

* Allow to reorder properties

* Fix isort

* Allow to opt-out for specific events

* Fix name clash between new and old field to make migration feasible

src/pretix/base/migrations/0250_eventmetaproperty_filter_public.py

@@ -0,0 +1,52 @@
+# Generated by Django 4.2.4 on 2023-10-31 10:08
+import i18nfield.fields
+from django.db import migrations, models
+
+import pretix.helpers.json
+
+
+def convert_allowed_values(apps, schema_editor):
+    EventMetaProperty = apps.get_model('pretixbase', 'EventMetaProperty')
+    for emp in EventMetaProperty.objects.filter(allowed_values__isnull=False):
+        emp.choices = [
+            {"key": _v.strip(), "label": {"en": _v.strip()}}
+            for _v in emp.allowed_values.splitlines()
+        ]
+        emp.save(update_fields=["choices"])
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("pretixbase", "0249_hidden_if_item_available"),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name="eventmetaproperty",
+            name="filter_public",
+            field=models.BooleanField(default=False),
+        ),
+        migrations.AddField(
+            model_name="eventmetaproperty",
+            name="public_label",
+            field=i18nfield.fields.I18nCharField(null=True),
+        ),
+        migrations.AddField(
+            model_name="eventmetaproperty",
+            name="position",
+            field=models.IntegerField(default=0),
+        ),
+        migrations.AddField(
+            model_name="eventmetaproperty",
+            name="choices",
+            field=models.JSONField(null=True, encoder=pretix.helpers.json.CustomJSONEncoder),
+        ),
+        migrations.RunPython(
+            convert_allowed_values,
+            migrations.RunPython.noop
+        ),
+        migrations.RemoveField(
+            model_name="eventmetaproperty",
+            name="allowed_values",
+        ),
+    ]