Set up CDN for crates.io's download statistics

[jdno]

The infra-team recently created an S3 bucket for crates.io so that it can export its daily downloads statistics from the database. The crates.io team wants to make these statistics publicly available, which requires us serve them through a CDN.

Two different options have been discussed:

1. Add the new bucket to static.crates.io as a new origin
2. Create a new CDN just for the statistics

No conclusion has been reached and resolving this discussion is one of the first tasks of this issue.

Tasks

• [ ] Explore both options and propose a solution to the infra-team
• [ ] Set up CDN in staging environment
• [ ] Confirm working functionality with crates.io team
• [ ] Set up CDN in production environment