Use config_export function instead of calling dokku as a subcommand

plugins/config/functions

@@ -0,0 +1,17 @@
+#!/usr/bin/env bash
+set -eo pipefail; [[ $DOKKU_TRACE ]] && set -x
+source "$PLUGIN_PATH/common/functions"
+
+config_export() {
+  local CONFIG_TYPE="$1"
+  local APP="$2"
+  local ENV_FILE="$DOKKU_ROOT/$APP/ENV"
+
+  [[ $CONFIG_TYPE == "global" ]] && ENV_FILE="$DOKKU_ROOT/ENV"
+  [[ ! -f $ENV_FILE ]] && return 0
+  [[ ! -s $ENV_FILE ]] && return 0
+
+  VARS=$(grep -Eo "export ([a-zA-Z_][a-zA-Z0-9_]*=.*)" $ENV_FILE | cut -d" " -f2-)
+  echo "$VARS" | awk '{print "export " $0}'
+  return 0
+}