nixos/photoprism: use nsenter to call photoprism bin with correct UID and PID

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

@@ -18,6 +18,9 @@ let
     in
     pkgs.writeShellScript "manage" ''
       ${setupEnv}
+      eval "$(${config.systemd.package}/bin/systemctl show -pUID,MainPID photoprism.service | ${pkgs.gnused}/bin/sed "s/UID/ServiceUID/")"
+      exec ${pkgs.util-linux}/bin/nsenter \
+        -t $MainPID -m -S $ServiceUID -G $ServiceUID --wdns=${cfg.storagePath} \
       exec ${cfg.package}/bin/photoprism "$@"
     '';
 in