Allow searching option descriptions

[jtojnar]

Searching by option name is great if you can roughly guess the option name but this is not always the case, especially for new users.

For example, the basic algorithm for determining how to install a package on NixOS (search for NixOS option; if it does not exist, use environment.systemPackages) fails for GSConnect because it is only mentioned in description of programs.kdeconnect.enable.

It would be nice to add a button to toggle between searching option names and full-text search.

[nixos-discourse]

This issue has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/gsconnect-does-not-work-with-gdm/46271/5