Summary:
Pull Request resolved: https://github.com/facebookresearch/pytorch3d/pull/1394

The bash logic for building conda packages became fiddly to edit. We need to switch cuda-toolkit to pytorch-cuda when PyTorch>=1.12 which was going to be a pain, so here I rewrite the code in python and do it.

Reviewed By: shapovalov

Differential Revision: D42036406

fbshipit-source-id: 8bb80c2f7545477182b23fc97c8514dcafcee176