To add VN_433 and VN_923 for Vietnam

This is to add VN_433 and VN_923 for Vietnam.

Main document: https://vanban.chinhphu.vn/default.aspx?pageid=27160&docid=204286
        Page 16: https://datafiles.chinhphu.vn/cpp/files/vbpq/2021/10/08-btttt.signed.pdf
        Item 39: 433.05 - 434.79 MHz <=25 mW ERP
        Item 45: 920 - 923 MHz <=25 mW ERP

meshtastic/config.proto

@@ -930,6 +930,14 @@ message Config {
        * Kazakhstan 863MHz
        */
       KZ_863 = 24;
+      /*
+       * Vietnam 433Mhz
+       */
+      VN_433 = 25;
+      /*
+       * Vietnam 923Mhz
+       */
+      VN_923 = 26; 
     }
 
     /*