refactor: allow the scheduler to decide if an app is deployed

Without moving this to the scheduler, all applications are assumed to not be deployed unless the scheduler is set to docker-local.

Closes #3531

plugins/common/functions

@@ -450,14 +450,10 @@ get_app_running_container_types() {
 is_deployed() {
   declare desc="return 0 if given app has a running container"
   local APP="$1"
-  if [[ -f "$DOKKU_ROOT/$APP/CONTAINER" ]] || [[ $(
-    ls "$DOKKU_ROOT/$APP"/CONTAINER.* &>/dev/null
-    echo $?
-  ) -eq 0 ]]; then
-    return 0
-  else
-    return 1
-  fi
+  source "$PLUGIN_AVAILABLE_PATH/config/functions"
+
+  local DOKKU_SCHEDULER=$(get_app_scheduler "$APP")
+  plugn trigger scheduler-is-deployed "$DOKKU_SCHEDULER" "$APP"
 }
 
 is_container_running() {