fix: ``down`` action is supported

We force ``--remove-orphans`` as it'll remove all the previous
dockers that have been launched in the same project. We don't
need to compute anything for this.

bin/compose

@@ -2505,7 +2505,7 @@ case "$action" in
     run)
         services="${action_posargs[0]}"
         ;;
-    "")
+    ""|down)
         services=
         ;;
     *)
@@ -2546,7 +2546,7 @@ case "$action" in
         full_init=true
         post_hook=true
         ;;
-    "")
+    ""|down)
         full_init=
         ;;
     *)
@@ -2604,6 +2604,10 @@ case "$action" in
         launch_docker_compose "${compose_opts[@]}" "$action" "${action_opts[@]}" "${remainder_args[@]}"
         warn "Runtime configuration modification (from relations) are not included here."
         ;;
+    down)
+        remainder_args+=("--remove-orphans")
+        launch_docker_compose "${compose_opts[@]}" "$action" "${action_opts[@]}" "${remainder_args[@]}"
+        ;;
     *)
         if [ "$is_service_action" ]; then
             run_service_action "$SERVICE_PACK" "$action" "${remainder_args[@]}"