public void fail(HttpClientResponse response) {
        long retryAfter = retrieveRetryAfterSeconds(response);
        HttpStatus status = HttpStatus.fromStatusCode(response.statusCode());
        fail(status, retryAfter);
    }
@return get current upstream. null if no upstream available
server/src/main/java/com/epam/aidial/core/server/upstream/UpstreamRoute.java