Added default temperature from ESP32 MCU and NRF52 MCU

Added NRF52Board.h and NRF52Board.cpp
Modified NRF52 variants to extend from NRF52Board to share common feature

examples/simple_repeater/MyMesh.cpp

@@ -173,6 +173,12 @@ int MyMesh::handleRequest(ClientInfo *sender, uint32_t sender_timestamp, uint8_t
 
     telemetry.reset();
     telemetry.addVoltage(TELEM_CHANNEL_SELF, (float)board.getBattMilliVolts() / 1000.0f);
+
+    float temperature = (float)board.getMCUTemperature();
+    if(!isnan(temperature)) { // Supported boards with built-in temperature sensor. ESP32-C3 may return NAN
+      telemetry.addTemperature(TELEM_CHANNEL_SELF, (float)board.getMCUTemperature()); // Built-in MCU Temperature
+    }
+
     // query other sensors -- target specific
     if ((sender->permissions & PERM_ACL_ROLE_MASK) == PERM_ACL_GUEST) {
       perm_mask = 0x00;  // just base telemetry allowed