Add post config update hook

This adds a hook that will send in the $APP, action name and config vars.

By adding this, we allow plugin creators to handle this kind of events as well.

Signed-off-by: Jeroen van Baarsen <jeroenvanbaarsen@gmail.com>

plugins/config/functions

@@ -187,6 +187,7 @@ ${var}"
     config_styled_hash "$ENV_ADD" "       "
 
     config_write "$ENV_TEMP"
+    plugn trigger post-config-update $APP "set" "$@"
   fi
 
   if [[ "$DOKKU_CONFIG_RESTART" == "true" ]]; then
@@ -218,6 +219,8 @@ config_unset() {
     [[ "$var" == "NO_VHOST" ]] && config_set --no-restart $APP NO_VHOST=0 && DOKKU_CONFIG_RESTART=true
   done
 
+  plugn trigger post-config-update $APP "unset" "$@"
+
   if [[ "$DOKKU_CONFIG_RESTART" == "true" ]]; then
     dokku_log_info1 "Restarting app $APP"
     dokku ps:restart $APP