Systemd gives us the ability to monitor backup job status using existing
monitoring solutions (node exporter) and allows us greater control over
the scheduling of the backup jobs.

This introduces a breaking change that requires users to manually remove
the old repositories from the clients and redeploying them with the
role. You will have to remove the Cron job that was created by the
Ansible script, everything else will be overwritten with a run from the
newer version.

- name: Remove backup cron jobs
  ansible.builtin.cron:
    name: BORG (Application level backups)
    state: absent
  become: true
- name: Remove env for backup cron job
  ansible.builtin.cron:
    name: BORG_PASSPHRASE
    env: true
    state: absent
  become: true

Performing manual migrations on the Borg server is not required.

We now additionally support multiple Borg repositories per client host
using the `borg_backup_argument` variable.

Signed-off-by: Colin Wilk <colin.wilk@tum.de>