[package] make torch.package produce unified format (#51826)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/51826
Looks like this:
```
resnet.pt
├── .data # Data folder named so it can't clash with torch.package codemodules.
│ │ # Names/extensions automatically added to avoid namingconflicts.
│ ├── 94286146172688.storage # tensor data
│ ├── 94286146172784.storage
│ ├── extern_modules # torch.package metadata
│ ├── version # version metadata
│ └── ...
├── model # package pickled model created w/
│ │ # exporter.save_pickel('model','model.pkl', resnet_model)
│ └── model.pkl
└── torchvision # all code dependencies for packaged picked
└── models # models are captured as source files
├── resnet.py
└── utils.py
```
Since `version` is hardcoded in our zip reader/writer implementation,
add it as an option that defaults to "version" but accepts other
locations for putting the version metadata.
Test Plan: Imported from OSS
Reviewed By: zdevito
Differential Revision: D26295649
Pulled By: suo
fbshipit-source-id: 2d75feeb7de0f78196b4d0b6e2b814a7d58bd1dd
