Merge branch 'rsync.net-account-migration' into 'master'

docs/backups.md

docs/ssh-hostkeys.txt

docs/ssh-known_hosts.txt

group_vars/all/vault_rsync.net.yml

host_vars/prio.ch-s012.rsync.net

host_vars/zh1905.rsync.net

hosts

misc/borg.sh

playbooks/rsync.net.yml

playbooks/tasks/sync-ssh-hostkeys.yml

roles/borg_client/defaults/main.yml

roles/borg_client/tasks/main.yml

roles/borg_client/templates/borg-backup.sh.j2

roles/borg_client/templates/borg.j2

roles/rsync_net/templates/authorized_keys.j2