The Rustup release process has historically been a manual process that
involved copying files from S3 to the local machine and back to S3. This
introduced a high risk of human error. When modifications to the
existing release script became necessary, the decision was made to
automate the release process (see rust-lang#3819 for details).

The documentation in the dev-guide has been updated to cover the new
release process, which is fully automated to produce `beta` releases
using GitHub Actions and the [promote-release] tooling.

[promote-release]: https://github.com/rust-lang/promote-release

Co-authored-by: rami3l <[email protected]>

Based on a discussion[^1] with the release team, the decision has been
made to create a new S3 bucket for Rustup build artifacts. This enable
us to revoke the access that Rustup's CI has to the release bucket,
improving security and reducing the risk of malicious or accidental
compromise of Rustup releases.

[^1]: rust-lang#3844 (comment)