Prepare ONNX export for torch v1.11
# What does this PR do?

This PR prepares the ONNX export for `torch` v1.11, where the following arguments from the [`torch.onnx.export()` ](https://pytorch.org/docs/stable/onnx.html#torch.onnx.export)function will be removed:

* `use_external_data_format`
* `enable_onnx_checker`

A simple check on the `torch` version is used to ensure backwards compatibility with versions < 1.11

I've also tested that the slow tests pass on the nightly version of `torch` by running:

```
RUN_SLOW=1 pytest tests/test_onnx_v2.py
```


_The documentation is not available anymore as the PR was closed or merged._