Send configuration commands through DOWNLINK

[pradeeka7]

I have added a code snippet to send downlink messages to RAK7205 (or RAK811 based). I have tested the code with RAK7205 and it worked well. With this code you can do the following things:

1. RESET the RAK7205 - You should send 04FF on port 8. For ChirpStack use the base 64 equivalent of the message (BP8=). Payload size is 2 bytes. 2, Set the SEND TIME INTERVAL - Send Type Code 01 along with the number of seconds on port 8. Payload size is 4 bytes. Eg: 0100003C means 01 is the type code. 00003C is equivalent to 60 in decimal.

Similarly you can implement most of the AT commands.