[CDS Toolkit] Receiving 500 from the transaction endpoint if the backend response payload contains no "transactions" filed

[imesh94]

The issue is occurred when trying to process the invalid backend response for id permanence processing. Following response should be returned. The http response code should still be 500 since it is an invalid response from the backend.

{
    "errors": [
        {
            "code": "urn:au-cds:error:cds-all:GeneralError/Unexpected",
            "title": "Unexpected Error",
            "detail": "Schema validation failed in the Response: [Path '/data'] Object has missing required properties ([\"transactions\"]),"
        }
    ]
}

ob-internal: https://github.com/wso2-enterprise/wso2-ob-internal/issues/1297