GREG-17: Duplicate check

This merge request contains a validation check that checks whether two person identities have the same type and value, if the type is not other. This is to avoid duplicates that are not expected in the person identity table.

greg/api/serializers/person.py

@@ -38,7 +38,7 @@ class PersonIdentitySerializer(serializers.ModelSerializer):
         model = PersonIdentity
         fields = "__all__"
 
-    def identity_duplicate_exists(self, identity_type: str, value: str) -> bool:
+    def is_duplicate(self, identity_type: str, value: str) -> bool:
         # If the type is other then it is allowed that two entries are the same, since
         # the text may be some generic text added by the sponsor
         if identity_type == PersonIdentity.IdentityType.OTHER: