[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/config_BT.h

@@ -27,8 +27,7 @@
 #define config_BT_h
 
 extern void setupBT();
-extern bool BTtoMQTT();
-extern void MQTTtoBT(char* topicOri, JsonObject& RFdata);
+extern void XtoBT(const char* topicOri, JsonObject& RFdata);
 extern void launchBTDiscovery(bool overrideDiscovery);
 extern void stopProcessing();
 extern String stateBTMeasures(bool);