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/login.nix

@@ -0,0 +1,21 @@
+{ pkgs, ... }:
+{
+  services.greetd = {
+    enable = true;
+    settings = {
+      initial_session.command = "sway";
+      # initial_session.user ="swarsel";
+      default_session.command = ''
+        ${pkgs.greetd.tuigreet}/bin/tuigreet \
+          --time \
+          --asterisks \
+          --user-menu \
+          --cmd sway
+      '';
+    };
+  };
+
+  environment.etc."greetd/environments".text = ''
+    sway
+  '';
+}