Added storage default help function

plugins/storage/subcommands/default

@@ -0,0 +1,12 @@
+#!/usr/bin/env bash
+set -eo pipefail; [[ $DOKKU_TRACE ]] && set -x
+source "$PLUGIN_CORE_AVAILABLE_PATH/common/functions"
+source "$PLUGIN_CORE_AVAILABLE_PATH/storage/functions"
+
+storage_main_cmd() {
+  declare desc="Display storage plugin help content"
+  local cmd="storage"
+  help_formatted
+}
+
+storage_main_cmd "$@"