Define composable command interface

Firmware/src/Messages/Composer.h

@@ -1,9 +1,21 @@
 #pragma once
 #include "Protocol.h"
+#include <etl/optional.h>
+#include <etl/span.h>
 #include <etl/string.h>
 
 namespace message {
 namespace composer {
+enum class ComposableType {
+  MESSAGE_LIGHTDATA,
+  MESSAGE_INFO,
+  MESSAGE_WARNING,
+  MESSAGE_ERROR,
+  MESSAGE_SUCCESS,
+  COMMAND_HELP,
+  COMMAND_VERSION,
+};
+using Composable = etl::pair<ComposableType, etl::optional<etl::span<uint8_t>>>;
 bool sendMessage(protocol::Message type, etl::string_view content);
 } // namespace composer
 } // namespace message