Variable LoRa Packet sizes on node as well as server side

[Praneethsvch]

Currently the LoRa packet size is a fixed size. Addition of different sensing technologies to the existing sensors would need extra bytes for new sensor measurements. Need to add new enhancement where the lora packet size depends on the number of sensors on the node. The idea is to send packet size as 1st byte and use this to format the packet on the server side.

[Praneethsvch]

Example using structs and unions and different datatypes:

https://www.thethingsnetwork.org/forum/t/how-to-efficiently-assemble-and-extract-a-mix-of-integer-and-float-data-for-ttn/22908

[Praneethsvch]

for simplicity, additional bytes are appended at the end of existing payload and decoded in the back-end