feat: Manage secrets w/ sops-nix

Closes #1

hosts/nixos-testbed/configuration.nix

@@ -8,7 +8,7 @@
   sydnix = {
     filesystemType = "btrfs";
 
-    gpg.enable = true;
+    # gpg.enable = true;
 
     users.users = [
       "crumb"
@@ -101,6 +101,9 @@
   services.openssh.enable = true;
   services.openssh.settings.PermitRootLogin = "yes";
 
+  # TODO: Move to defaults.
+  users.mutableUsers = false;
+
   # services.xserver.windowManager.qtile = {
   #   enable = true;
   #   extraPackages = python3Packages: with python3Packages; [