nixos.photoprism: Relax sandbox to allow running exiftool

exiftool is written in Perl which appears to call `chown` as part of startup. This is blocked by the `@privileged` system call group. This causes a failure when changing image orientation.

Fixes: https://github.com/NixOS/nixpkgs/issues/249120

nixos/modules/services/web-apps/photoprism.nix

···
         RestrictNamespaces = true;
         RestrictRealtime = true;
         SystemCallArchitectures = "native";
-        SystemCallFilter = [ "@system-service" "~@privileged @setuid @keyring" ];
+        SystemCallFilter = [ "@system-service" "~@setuid @keyring" ];
         UMask = "0066";
       } // lib.optionalAttrs (cfg.port < 1024) {
         AmbientCapabilities = [ "CAP_NET_BIND_SERVICE" ];