feat: improve error management to avoid infinite loop

The device goes in deep sleep after 3 restarts when connection is not
successful

lib/Transmitter/LoRaTransmitter.h

@@ -22,9 +22,9 @@ public:
         uint8_t* appKey
     );
 
-    void init()                              override;
-    void join()                              override;
-    void send(uint8_t* payload, size_t size) override;
+    TransmitError init()                              override;
+    TransmitError join()                              override;
+    TransmitError send(uint8_t* payload, size_t size) override;
 
 private:
     uint64_t _joinEUI;