bug#43049: Add the ability to install GuixSD offline + Add the ability to add static IP

[bo0od]

Add the ability to install GuixSD offline + Add the ability to add 
static IP in the installation process.

This is important as users with static IP or using VMs or Offline usage 
cant use this distro.

These features are very common and its almost in every OS available, 
Hope to see it here as well.

ThX!