treewide: impermanence configuration

hosts/vps1/headscale.nix

@@ -48,6 +48,13 @@ in
     };
   };
 
+  environment.persistence."/persist".directories = [
+    {
+      directory = "/var/lib/headscale";
+      inherit (config.services.headscale) user group;
+    }
+  ];
+
   services.nginx.virtualHosts = {
     "${domain}" = {
       forceSSL = true;