Add squid proxy as egress cache (#62103)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/62103
This PR adds a squid proxy that's deployed dedicated for PyTorch CI. Initially we only roll out to GHA, and if things are ok we will extend this to circleci tests if necessary.
`http_proxy` and `https_proxy` are compatible with the following http clients:
- curl
- wget
- python
Existing cache policy:
```
refresh_pattern -i .(7z|deb|rpm|exe|zip|tar|tgz|gz|ram|rar|bin|tiff|bz2|run|csv|sh)$ 1440 80% 2880
```
It uses the standard squid refresh_pattern for cache requests. In our setup, we tried
to cache at least (1440 minutes - 1 day) and at max (2880 minutes - 2 days), with
last-modified factor 80% ([squid doc](http://www.squid-cache.org/Doc/config/refresh_pattern/)). Please refer to [pytorch/test-infra](https://github.com/pytorch/test-infra/tree/master/aws/websites/squid-proxy) for details.
Right now, it only applies to the `build` and `test` step, to limit the scope and make sure build and test are more reliable with egress cache.
Test Plan: Imported from OSS
Reviewed By: jbschlosser, malfet, seemethere, janeyx99
Differential Revision: D29892919
Pulled By: zhouzhuojie
fbshipit-source-id: ac17227f2553ca62881711b3e9943488dfd8defd
