Show renamed options properly

[ncfavier]

See https://github.com/NixOS/nixpkgs/issues/164453: obsolete options like networking.interfaces.<name>.ipAddress are displayed (poorly) in nixos-search, while they are absent from the nixos manual.

We should either remove them, or make it clear that the option was renamed and link to the new option.

[garbas]

:+1: we should definitely show that an option was renamed and provide a link to new option.

@ncfavier Is this information exposed in our export json?

[ncfavier]

No, this would require changes to the nixpkgs module system to tag renamed options with the old option's name.

I probably won't have time to work on that before a while.

[garbas]

Np. Lets keep it in our backlog