Depends on #7116 and #7121.

#7121 set up a source mirror for Spack. This adds to the release process so that binaries are also released. The upload of release tarballs to an S3 store should happen once a release branch is merged to master, so that binaries are available to users and so that they can be the default install mechanism.

• Once the release is merged to master, binaries are deployed to the public S3 binary mirror.