[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_SERIAL.h

@@ -27,8 +27,8 @@
 #define config_SERIAL_h
 
 extern void setupSERIAL();
-extern void SERIALtoMQTT();
-extern void XtoSERIAL(const char* topicOri, JsonObject& SERIALdata);
+extern void SERIALtoX();
+extern bool XtoSERIAL(const char* topicOri, JsonObject& SERIALdata);
 
 /*-------------------SERIAL topics & parameters----------------------*/
 
@@ -66,7 +66,7 @@ extern void XtoSERIAL(const char* topicOri, JsonObject& SERIALdata);
 #define SERIALmaxJSONlevel 2 // Max nested level in which JSON keys are converted to seperate sub-topics
 
 // settings for MQTT to SERIAL
-#define subjectXtoSERIAL "/commands/XtoSERIAL"
+#define subjectMQTTtoSERIAL "/commands/MQTTtoSERIAL"
 #ifndef SERIALPre
 #  define SERIALPre "00" // The prefix for the SERIAL message
 #endif