use espMqttClient, qos2 fixed

lib/espMqttClient/src/Packets/String.h

@@ -0,0 +1,22 @@
+/*
+Copyright (c) 2022 Bert Melis. All rights reserved.
+
+This work is licensed under the terms of the MIT license.  
+For a copy, see <https://opensource.org/licenses/MIT> or
+the LICENSE file.
+*/
+
+#pragma once
+
+#include <stdint.h>
+#include <cstring>  // memcpy
+
+#include "../Logging.h"
+
+namespace espMqttClientInternals {
+
+// encodes the given source string into destination and returns number of bytes used
+// destination is expected to be large enough to hold the number of bytes needed
+size_t encodeString(const char* source, uint8_t* dest);
+
+}  // namespace espMqttClientInternals