poppler: build with nss by default for signature support (#124294)
poppler: build with nss by default for signature support (#124294)

Since 21.01, poppler supports PDF signing. As applications like okular
start to make use of that feature, nss support for poppler is enabled by
default to avoid unnecessary package duplication.
When building a `minimal` version of poppler, nss is disabled as well.

closes #120928
NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs