new: [rsync-backup] add ``compose.yml`` to backup

Signed-off-by: Valentin Lab <valentin.lab@kalysto.org>

rsync-backup/hooks/schedule_command-relation-joined

@@ -41,6 +41,7 @@ $schedule    root   lock $label -v -D -p 10 -k -c "\
         -v \"$RSYNC_CONFIG_DIR:/etc/rsync\" \
         -v \"$host_path_key:$local_path_key\" \
         -v \"$HOST_DATASTORE:/mnt/source\" \
+        -v \"$HOST_COMPOSE_YML_FILE:/mnt/source/compose.yml\" \
         --network ${PROJECT_NAME}_default \
         \"$DOCKER_BASE_IMAGE\" \
         /mnt/source \"$target\"" 2>&1 | ts '\%F \%T' >> /var/log/cron/${label}_script.log