Enable systemd-boot/gummiboot boot-counting when it is released in `24.11` or `unstable`

https://github.com/NixOS/nixpkgs/pull/330017
https://github.com/NixOS/nixpkgs/blob/master/nixos/modules/system/boot/loader/systemd-boot/boot-counting.md

Enabled with the following:
```nix
boot.loader.systemd-boot.enable = true;
boot.loader.systemd-boot.bootCounting = true;
```