support kerberos/krb5 configuration

[ahgraber]

I would like to be able to configure my kerberos setup with nix-darwin. NixOS has krb5 options to configure the krb.conf file (https://github.com/NixOS/nixpkgs/blob/nixos-23.05/nixos/modules/config/krb5/default.nix) that are not present in nix-darwin.

I am completely new to the nix ecosystem (have barely gotten a configuration working), so I am unsure of whether we can simply port the nixos/modules/config/krb5 to nix-darwin/modules/services/krb5 or if there is significantly more development work required...

Thank you for considering!