Add script to compare namespace content for release cleanup (#51685)
Summary:
Usage explanation will be in the release note runbook.
This allows to generate diffs like:
```
Processing torch.nn
Things that were added:
{'quantizable', 'ChannelShuffle', 'LazyConvTranspose2d', 'LazyConv2d', 'LazyConvTranspose3d', 'LazyConv1d', 'GaussianNLLLoss', 'LazyConv3d', 'PixelUnshuffle', 'UninitializedParameter', 'LazyLinear', 'LazyConvTranspose1d'}
Things that were removed:
set()
```
This can then be shared with module owners along with the commits to help them validate that the namespace changes for their submodule is as expected.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/51685
Reviewed By: zhangguanheng66
Differential Revision: D26260258
Pulled By: albanD
fbshipit-source-id: 40e40f86314e17246899d01ffa4b2631e93b52f7
