[CI] Script to fetch creds from current AWS session (#121426)
Because some implementations, like OpenDAL does not work with AWS IMDSv2, but this script will bridge the gap and enables more recent `sccache` releases(that switched from simple-s3 to OpenDAL) to work in current CI system
When launched it prints something like:
```
export AWS_ACCESS_KEY_ID=XXXXX
export AWS_SECRET_ACCESS_KEY=YYYY
export AWS_SESSION_TOKEN=ZZZZ
```
which can be `eval`ed and passed then sccache can use those failures.
Validated in https://github.com/pytorch/pytorch/pull/121323
Pull Request resolved: https://github.com/pytorch/pytorch/pull/121426
Approved by: https://github.com/Skylion007
