make update message adjustable by provider

include/Env.h

@@ -0,0 +1,16 @@
+#pragma once
+
+#include <optional>
+#include <string>
+namespace Env {
+
+enum class Key {
+    // provider settings
+    PROVIDER_UPDATE_MESSAGE,
+};
+
+std::optional<std::string> Get(Key key);
+
+std::string_view ToString(Key key);
+
+}