Add custom unassigned return code test when issue fixed

If after https://github.com/Kuadrant/kuadrant-operator/issues/1022 / https://issues.redhat.com/browse/CONNLINK-287 is solved, and it will be possible to return custom [unassigned](https://www.iana.org/assignments/http-status-codes/http-status-codes.xhtml) return codes with authpolicy, create test returning this custom return code

Tests for valid return codes located at `testsuite/tests/singlecluster/authorino/response/test_deny_with.py`

Wait for issue 1022 and CONNLINK-287 to be resolved, then read testsuite/tests/singlecluster/authorino/response/test_deny_with.py, which contains tests for valid return codes. Add a test for a custom unassigned return code with authpolicy and run the relevant response tests to confirm it passes.

Written by the indexing model from the issue text.