HuggingFace Estimator requires `py_version` when `image_uri` is specified

[j-adamczyk]

Describe the bug

As per documentation, HuggingFace Estimator requires providing py_version argument when image_uri argument is specified. It should not, since when I point to a specific image, this argument doesn't matter. Curiously, transformers_version and pytorch_version are, properly, not required then.

[akrishna1995]

We have added your feature request to our backlog of feature requests and may consider putting it into future SDK versions. I will go ahead and close the issue now, please let me know if you have any more feedback.