private static Onnx.TensorProto getConstantTensor(String name, Onnx.GraphProto graph) {
        for (Onnx.TensorProto tensorProto : graph.getInitializerList()) {
            if (tensorProto.getName().equals(name)) {
                return tensorProto;
            }
        }
        return null;
    }
Converts an ONNX graph to a Vespa IntermediateGraph which is the basis
for generating Vespa ranking expressions.

@author lesters
model-integration/src/main/java/ai/vespa/rankingexpression/importer/onnx/GraphImporter.java