Add Hardware Type: BetaFPV 900 Nano TX (#307)

Fairly simple, this just adds a new type to the hardware types in mesh.proto for the [BetaFPV Nano 900 TX](https://betafpv.com/products/elrs-nano-tx-module)

meshtastic/mesh.proto

@@ -378,6 +378,11 @@ enum HardwareModel {
    */
   BETAFPV_2400_TX = 45;
   
+  /*
+   * BetaFPV ExpressLRS "Nano" TX Module 900MHz with ESP32 CPU
+   */
+   BETAFPV_900_NANO_TX = 46;
+  
   /*
    * Reserved ID For developing private Ports. These will show up in live traffic sparsely, so we can use a high number. Keep it within 8 bits.
    */