feat(main): Add configurable VIES-offline fallback policy

upgrade/upgrade-1.0.3.php

@@ -0,0 +1,12 @@
+<?php
+
+use Websmid\VatCheck\Config\Config;
+
+if (!defined('_PS_VERSION_')) {
+    exit;
+}
+
+function upgrade_module_1_0_3($module)
+{
+    return Configuration::updateValue(Config::OFFLINE_MODE_CONFIG_KEY, Config::OFFLINE_MODE_DEFAULT);
+}