private static String createContextKey(String onnxName, Map<String, TensorType> inputTypes) {
        StringBuilder key = new StringBuilder().append(onnxName).append(":");
        inputTypes.entrySet().stream().sorted(Map.Entry.comparingByKey())
                .forEachOrdered(e -> key.append(e.getKey()).append(":").append(e.getValue()).append(","));
        return key.substring(0, key.length()-1);
    }
Defers to 'vespa-analyze-onnx-model' to determine the output type given
a set of inputs. For situations with symbolic dimension sizes that can't
easily be determined.

@author lesters
config-model/src/main/java/com/yahoo/vespa/model/ml/OnnxModelProbe.java