Spike: create onnxruntime + PyTorch dev container

Example changes to explore dev container to easily build PyTorch from source and consume this in onnxruntime.

There are some other options to consider here:

• Multiple Dev Container definitions (if we want to support different environments for different onnxruntime workstreams)
• Move PyTorch environment setup into a self contained script. This would let developer decide whether they want PyTorch source (as opposed to PyTorch installed from PIP)