lib/network: adds symlink to configure systemd-resovled properly

[wahrwolf]

When "Copy network config from ISO" is selected, it sets up systemd-resolved and systemd-networkd, however, systemd-resolved requires resolve.conf to be a stub in order to work properly.

This PR addresses the issue that it's currently not a stub, but a core filesystem file meant for other types of resolvers.

[svartkanin]

Can you provide a description of the PR and the problem

[Torxed]

Can you provide a description of the PR and the problem

I filled in the blanks as I forced poor @wahrwolf to submit this PR 😅 Sorry for the confusion!

[wahrwolf]

I tested the change and after the first reboot resolvectl status confirms the stub-resolver

Here is the weird part:
From the iso live system the symlink looks fine.
However if you chroot into the system after the archinstall script finished, the symlinks is not correctly displayed.
Both file and ls detect it as a local ascii file.
Tbh I do not understand it and it hints to something weird with os.symlink, the arch-chroot script, ext4 or all together.

Everything looks normal after the reboot, so I assume this can be safely ignored