refactor: split common/nixos.nix and -/home.nix

Split these big files into modular files that
are easier to share and read on their own.

profiles/common/nixos/users.nix

@@ -0,0 +1,13 @@
+{ pkgs, config, ... }:
+{
+  users = {
+    mutableUsers = false;
+    users.swarsel = {
+      isNormalUser = true;
+      description = "Leon S";
+      hashedPasswordFile = config.sops.secrets.swarseluser.path;
+      extraGroups = [ "networkmanager" "wheel" "lp" "audio" "video" "vboxusers" "scanner" ];
+      packages = with pkgs; [ ];
+    };
+  };
+}