[package] Create API reference (#55812)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/55812
**Summary**
This commit creates a barebones API reference doc for `torch.package`.
The content is sourced from the docstrings in the source for the
`torch.package`.
**Test Plan**
Continuous integration (specifically the docs tests).
Test Plan: Imported from OSS
Reviewed By: gmagogsfm
Differential Revision: D27726816
Pulled By: SplitInfinity
fbshipit-source-id: 5e9194536f80507e337b81c5ec3b5635d7121818
