Upload the regression file to Amazon S3 (#1679)
Summary:
When a regression happens, we should also upload the regression detector output to S3.
Pull Request resolved: https://github.com/pytorch/benchmark/pull/1679
Test Plan:
Local testing:
```
$ python ./scripts/userbenchmark/upload_s3.py --userbenchmark_json $LATEST_REGRESSION_RESULT --userbenchmark_platform "gcp_a100"
```
Reviewed By: janeyx99
Differential Revision: D46107344
Pulled By: xuzhao9
fbshipit-source-id: 5212f978f54d24f78483e9ccddc8801a00a45e7f
