[MQTT] Added Arduino String overload

src/protocols/MQTT.cpp

@@ -145,6 +145,10 @@ int16_t MQTTClient::disconnect() {
   return(_tl->closeTransportConnection());
 }
 
+int16_t MQTTClient::publish(String& topic, String& message) {
+  return(MQTTClient::publish(topic.c_str(), message.c_str()));
+}
+
 int16_t MQTTClient::publish(const char* topic, const char* message) {
   // encode packet length
   size_t topicLen = strlen(topic);

src/protocols/MQTT.h

@@ -35,6 +35,7 @@ class MQTTClient {
     // basic methods
     int16_t connect(const char* host, const char* clientId, const char* userName = "", const char* password = "", uint16_t keepAlive = 60, bool cleanSession = true, const char* willTopic = "", const char* willMessage = "");
     int16_t disconnect();
+    int16_t publish(String& topic, String& message);
     int16_t publish(const char* topic, const char* message);
     int16_t subscribe(const char* topicFilter);
     int16_t unsubscribe(const char* topicFilter);