Script to validate converting Fixed -> Dynamic shape ONNX model

[rmccorm4]

It's possible to edit an ONNX graph and change certain shapes, such as batch size, to -1 to create a dynamic shape model from an existing fixed shape model.

However, this isn't guaranteed to work in all cases, especially if a model contains any hard-coded shapes in an intermediate layer or something.

It would be nice to have a script that compares the output of the fixed shape and dynamic shape models for the same input shape, as well as for a larger batch size of identical inputs to make sure that the output for the whole batch is computed correctly.