Common configuration file for rt-mbms-modem and rt-mbms-mw

## Description
The [rt-mbms-modem](https://github.com/5G-MAG/rt-mbms-modem) and the [rt-mbms-mw](https://github.com/5G-MAG/rt-mbms-mw) share a common [configuration file](https://github.com/5G-MAG/rt-mbms-mw/blob/development/supporting_files/5gmag-rt.conf). This file should be moved to this repository to have a single point of truth for both projects.