[SERIAL] Enable SERIAL to X communication (#2068)

Add Serial as a communication layer so as to transmit data to/from serial
Enable discovery of BT sensors through serial
Add serial heartbeat

Change discovery principle for interval and intervalacts, keep them always discovered and deactivate adaptivescan when changed. Instead of removing their discovery when adaptive scan is activated

Increase JSON_MSG_BUFFER_MAX as we are now using const char* and it requires more memory for Arduino Json Deserialization

Co-authored-by: Florian <1technophile@users.noreply.github.com>

main/Zgateway2G.ino

@@ -76,7 +76,7 @@ void signalStrengthAnalysis() {
   }
 }
 
-bool _2GtoMQTT() {
+bool _2GtoX() {
   // Get the memory locations of unread SMS messages.
   unreadSMSNum = A6l.getUnreadSMSLocs(unreadSMSLocs, 512);
   Log.trace(F("Creating SMS  buffer" CR));
@@ -96,7 +96,7 @@ bool _2GtoMQTT() {
   return false;
 }
 #  if simpleReceiving
-void MQTTto2G(char* topicOri, char* datacallback) {
+void Xto2G(const char* topicOri, const char* datacallback) {
   String data = datacallback;
   String topic = topicOri;
 
@@ -127,7 +127,7 @@ void MQTTto2G(char* topicOri, char* datacallback) {
 #  endif
 
 #  if jsonReceiving
-void MQTTto2G(char* topicOri, JsonObject& SMSdata) {
+void Xto2G(const char* topicOri, JsonObject& SMSdata) {
   if (cmpToMainTopic(topicOri, subjectMQTTto2G)) {
     const char* sms = SMSdata["message"];
     const char* phone = SMSdata["phone"];