[RN8209] Add task WDT (#1657)

Add WDT and reduce update as we now have a change based pub mechanism
Base the change detection on current rather than power and simplify it
Round the result to 2 digits after comma
Add docs

main/main.ino

@@ -338,6 +338,14 @@ long value_from_hex_data(const char* service_data, int offset, int data_length,
   return value;
 }
 
+/*
+ rounds a number to 2 decimal places
+ example: round(3.14159) -> 3.14
+*/
+double round2(double value) {
+  return (int)(value * 100 + 0.5) / 100.0;
+}
+
 /*
 From an hexa char array ("A220EE...") to a byte array (half the size)
  */