Modernize zeroconf disablement

I think this can be done via native NetworkManager features now for modern RHELs and Fedoras:

```
RUN { echo 'NETWORKING=yes'; echo 'NOZEROCONF=yes'; } >> /etc/sysconfig/network
```

Initially I made an attempt to do this in bootc but spinning an issue so I can take a look later:

https://github.com/osbuild/bootc-foundry/pull/36