Switch from vostok to Hetzner Storagebox

Context: https://lists.archlinux.org/pipermail/arch-devops/2020-June/000407.html

vostok is rapidly getting full. Also, it's too small to handle backing up the archive.

We've decided to switch to a big storagebox from Hetzner as it should free us from some server maintenance duties.

Tasks:

• Order the storagebox
• Set up the storagebox
• Migrate old backup data from vostok to storagebox
• Prepare Ansible changes
• Add archive to backup
• Roll out Ansible changes to all servers
• Decommission vostok