Feature: Support for AU_915_923 FSB in LoRaWAN concentrators

[kbeaugrand]

Is your feature request related to a problem? Please describe.
When deploying to Australia, we need to support AU 915-923 frequencies on the portal.

Describe the solution you'd like
The LoRa WAN Starter kit already supports 915-923 FSB. We need to implement the router config files for the portal sur support it in the web interface.

Describe alternatives you've considered
N/A

Additional context
N/A