move deploy key to host config, add ralph and benjamin users

- Move forgejo-deploy pubkey from users/steffen to hosts/cryodev-main/
  (deploy key belongs to the host, not a user)
- Remove deploy key from steffen's authorized keys
- Add users ralph and benjamin (pubkeys pending)
- Register both new users in cryodev-main host config

users/benjamin/default.nix

@@ -0,0 +1,11 @@
+{
+  normalUsers.benjamin = {
+    extraGroups = [
+      "wheel"
+    ];
+    sshKeyFiles = [
+      # TODO: Add benjamin's public key
+      # ./pubkeys/benjamin.pub
+    ];
+  };
+}