Add unattended installer and setup

[hbjorgo]

Please add the possibility to run the installer and gateway-config unattended. This will make it much easier to setup a gateway through automation tools like Ansible for example.

• sudo ./install.sh --board "RAKxxxx"
• sudo gateway-config --password "PWD" --frequency-plan 868
  and so on.

[Sheng2216]

You can check out the "udp docker" repository at this link: https://github.com/RAKWireless/udp-packet-forwarder. If you have Docker installed on your device, you can take advantage of the Dockerized version of the udp-packet forwarder by running the following command:
docker run --privileged -v ./global_conf.json:/app/global_conf.json:ro --name udp-packet-forwarder -e MODEL=RAK7248 rakwireless/udp-packet-forwarder:latest
Make sure to replace global_conf.json with the name of your configuration file and MODEL with the model of your device.
you can pass in as many environments variables as you want to configure the service, check the environment variable section in the readme for more details