[torch vitals] Initial implementation (#51047)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/51047
If the environment variable `TORCH_VITAL` is set to a non-zero length string, the vitals a dumped at program end.
The API is very similar to google's logging
Test Plan: buck test //caffe2/aten:vitals
Reviewed By: bitfort
Differential Revision: D25791248
fbshipit-source-id: 0b40da7d22c31d2c4b2094f0dcb1229a35338ac2
