Decommission buse.tails.boum.org

Now that we've migrated to GitLab, we should decommission buse so that:

• Riseup folks can get rid of the obsolete virtualization host buse is running on.
• We stop paying for the hosting of that VM.

Steps:

• backup Redmine database + current installation (including plugins) + attachments directory
• follow sysadmin doc for decommissioning a system
• Consider wiping data
• power off buse.tails.boum.org
• wait a day or two to identify any unknown dependency of our infra/workflow on buse.tails.boum.org
• ask Riseup to destroy the VM
• tell our accounting team about the decommissioning date
• Consider deleting backups ("Cleaning up backups" in sysadmin.git:backups.mdwn)