🚚 [#4606] Move CatalogueSerializer to shared library code

Objects API and ZGW APIs registration backends both use the same
option structure for the catalogue, so we can re-use the serializer to
have a single source of truth.

src/openforms/contrib/zgw/serializers.py

@@ -0,0 +1,44 @@
+from django.utils.translation import gettext_lazy as _
+
+from rest_framework import serializers
+
+from openforms.api.validators import AllOrNoneTruthyFieldsValidator
+from openforms.utils.validators import RSINValidator, validate_uppercase
+
+
+class CatalogueSerializer(serializers.Serializer):
+    """
+    Specify which catalogue to use to look up case/document types.
+
+    Certain configuration models also define default fields like ``catalogue_domain``
+    and ``catalogue_rsin`` to fall back on, such as:
+
+    - :class:`openforms.registrations.contrib.objects_api.models.ObjectsAPIGroupConfig`
+    - :class:`openforms.registrations.contrib.zgw_apis.models.ZGWApiGroupConfig`
+    """
+
+    domain = serializers.CharField(
+        label=_("domain"),
+        required=False,
+        max_length=5,
+        help_text=_(
+            "The 'domein' attribute for the Catalogus resource in the Catalogi API."
+        ),
+        default="",
+        validators=[validate_uppercase],
+    )
+    rsin = serializers.CharField(
+        label=_("RSIN"),
+        required=False,
+        max_length=9,
+        validators=[RSINValidator()],
+        help_text=_(
+            "The 'rsin' attribute for the Catalogus resource in the Catalogi API."
+        ),
+        default="",
+    )
+
+    class Meta:
+        validators = [
+            AllOrNoneTruthyFieldsValidator("domain", "rsin"),
+        ]

src/openforms/registrations/contrib/objects_api/config.py

@@ -10,11 +10,11 @@
 
 from openforms.api.fields import PrimaryKeyRelatedAsChoicesField
 from openforms.api.utils import get_from_serializer_data_or_instance
-from openforms.api.validators import AllOrNoneTruthyFieldsValidator
+from openforms.contrib.zgw.serializers import CatalogueSerializer
 from openforms.formio.api.fields import FormioVariableKeyField
 from openforms.template.validators import DjangoTemplateValidator
 from openforms.utils.mixins import JsonSchemaSerializerMixin
-from openforms.utils.validators import RSINValidator, validate_rsin, validate_uppercase
+from openforms.utils.validators import validate_rsin
 
 from .client import get_catalogi_client, get_objecttypes_client
 from .models import ObjectsAPIGroupConfig
@@ -26,41 +26,6 @@ class VersionChoices(IntegerChoices):
     V2 = 2, _("v2, variables mapping")
 
 
-class CatalogueSerializer(serializers.Serializer):
-    """
-    Specify which catalogus to use to look up document types.
-
-    This matches the fields ``catalogue_domain`` and ``catalogue_rsin`` on the
-    :class:`ObjectsAPIGroupConfig` model.
-    """
-
-    domain = serializers.CharField(
-        label=_("domain"),
-        required=False,
-        max_length=5,
-        help_text=_(
-            "The 'domein' attribute for the Catalogus resource in the Catalogi API."
-        ),
-        default="",
-        validators=[validate_uppercase],
-    )
-    rsin = serializers.CharField(
-        label=_("RSIN"),
-        required=False,
-        max_length=9,
-        validators=[RSINValidator()],
-        help_text=_(
-            "The 'rsin' attribute for the Catalogus resource in the Catalogi API."
-        ),
-        default="",
-    )
-
-    class Meta:
-        validators = [
-            AllOrNoneTruthyFieldsValidator("domain", "rsin"),
-        ]
-
-
 @extend_schema_serializer(
     examples=[
         OpenApiExample(