private static boolean isSignatureOutput(ImportedModel model, IntermediateOperation operation) {
        for (ImportedModel.Signature signature : model.signatures().values()) {
            for (String outputName : signature.outputs().values()) {
                if (outputName.equals(operation.name())) {
                    return true;
                }
            }
        }
        return false;
    }
Takes an IntermediateGraph and converts it to a ImportedModel containing
the actual Vespa ranking expressions.
model-integration/src/main/java/ai/vespa/rankingexpression/importer/ModelImporter.java