Add an ONNX model with dynamic shape for the example

[rmccorm4]

Current example is a fixed-shape Resnet50 from ONNX model zoo.

This doesn't work with dynamic shape and optimization profile examples.

Maybe use Alexnet example from here instead and update README and tutorial: https://gist.github.com/rmccorm4/b72abac18aed6be4c1725db18eba4930

[skullbaselab]

Cool. It was nice working with you at GTC