Enhance the OSD test program

[pkendall64]

Adds debug message for OSD commands in VRx code

I'm thinking of extending this "test" program to be able to send all of the MSP commands to the VRx

[lesharodin]

Thanks, it works. With help of @pkendall64 there is some short usage manual:

1. Flash esp32/esp8266 with DEBUG_ESP/32_TX_BACKPACK
   Dont forget to add binding phrase to user_defines
2. Run python osd_test.py
   usage:
   send <row> <col> <message> e.g. 5 0 HELLO WORLD
   send d for display messages
   send c to clear display buffer
   Use only UPPERCASE letters for messages