feat(lvm_self_backup): Add error service when systemd service fails

This is to be notified when the systemd service fails to e.g. unmount the partition.

roles/lvm_self_backup/tasks/main.yml

@@ -55,7 +55,7 @@
       dest: "/usr/local/bin/backup-lvm-ls"
   become: true
 
-- name: Install backup service & timer.
+- name: Install backup services & timer.
   ansible.builtin.template:
     src: "{{ item }}"
     dest: /etc/systemd/system/
@@ -63,6 +63,7 @@
     owner: "root"
     group: "root"
   with_items:
+    - "backup-error.service"
     - "backup-lvm.service"
     - "backup-lvm.timer"
   notify: Reload systemd config

roles/lvm_self_backup/templates/backup-error.service

@@ -0,0 +1,6 @@
+[Unit]
+Description=Writes the error for the monitoring to pick the failure up.
+
+[Service]
+Type=oneshot
+ExecStart=/usr/bin/bash -c 'echo 1337 > {{ lvm_self_backup_status_directory }}/backup.status && chown {{ lvm_self_backup_status_directory_uid }}:{{ lvm_self_backup_status_directory_gid }} {{ lvm_self_backup_status_directory }}/backup.status'