[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_PWM.h

@@ -27,7 +27,7 @@
 
 extern void setupPWM();
 extern void PWMLoop();
-extern void MQTTtoPWM(char*, JsonObject&);
+extern void XtoPWM(const char*, JsonObject&);
 
 #define subjectMQTTtoPWM          "/commands/MQTTtoPWM"
 #define subjectMQTTtoPWMset       subjectMQTTtoPWM "/set" //set channel(s) with JSON struct {"r":0-1,"g":0-1,"b":0-1,"w0":0-1,"w0":0-1,"fade":<fade time in seconds>}