nice and ionice to restic backup

roles/stable/restic/templates/restic-backup.service.j2

@@ -7,6 +7,10 @@ User={{ restic_user }}
 
 CPUQuota={{ 25 * ansible_processor_vcpus }}%
 
+Nice=19
+IOSchedulingClass=best-effort
+IOSchedulingPriority=7
+
 {% if restic_ssh_enabled %}
 Environment="RESTIC_REPOSITORY=sftp:{{ restic_ssh_host }}:{{ restic_repository_name }}"
 {% else %}