Create a build variant without propertary libs for fdroid

[PeterHasse]

According to https://f-droid.org/docs/Inclusion_Policy/ we need a build variant that can be build with
e.g. microG https://github.com/microg/GmsCore/wiki .

We only use GMS for the location service and this is also capsulated in the Data Provider.

[PeterHasse]

On a FP5 with lineageOS an microG we have the following warning. This is still the unmodified version of OMNT using GMS

2024-06-18 15:23:38.185 23552-23582 GooglePlayServicesUtil  de....okus.OpenMobileNetworkToolkit  W  de.fraunhofer.fokus.OpenMobileNetworkToolkit requires the Google Play Store, but it is missing.
2024-06-18 15:23:38.186 23552-23582 GoogleApiManager        de....okus.OpenMobileNetworkToolkit  W  The service for com.google.android.gms.common.internal.service.zap is not available: ConnectionResult{statusCode=SERVICE_INVALID, resolution=null, message=null}
2024-06-18 15:23:38.187 23552-23582 GooglePlayServicesUtil  de....okus.OpenMobileNetworkToolkit  W  de.fraunhofer.fokus.OpenMobileNetworkToolkit requires the Google Play Store, but it is missing.
2024-06-18 15:23:38.187 23552-23582 GoogleApiManager        de....okus.OpenMobileNetworkToolkit  W  The service for com.google.android.gms.common.internal.service.zap is not available: ConnectionResult{statusCode=SERVICE_INVALID, resolution=null, message=null}