Use `download_utils#template` and backup downloads

download_utils@1.1.0 includes the download_template extension which can be used to download multi-arch binaries with a clean API and allow an easy way to upload the files to GitLab package registry.

We should change our downloads to use the API and mirror the binaries into the generic package registry so that we reduce bandwidth for upstream and have, more importantly, have backups for any dependencies.