doc/rl-2505: move `services.dex` entry to other notable changes

- NixOS now has initial support for the [**COSMIC DE**](https://system76.com/cosmic) which is currently at **Alpha 7**. COSMIC is a Rust-based Desktop Environment by System76, makers of Pop!_OS. You can use COSMIC by enabling the greeter (login manager) with [](#opt-services.displayManager.cosmic-greeter.enable), and the DE itself by enabling [](#opt-services.desktopManager.cosmic.enable). The support in NixOS/Nixpkgs is stable but still considered experimental because of the recent the addition. The COSMIC maintainers will be waiting for one more release of NixOS to determine if the experimental tag should be removed or not. Until then, please report any issues to the [COSMIC DE tracker in Nixpkgs](https://github.com/NixOS/nixpkgs/issues/259641) instead of upstream.

- `services.dex` now restarts upon changes to the `.environmentFile` or entries in `.settings.staticClients[].secretFile` when the entry is a `path` type.

- `nixos-rebuild-ng`, a full rewrite of `nixos-rebuild` in Python, is available for testing. You can enable it by setting [](#opt-system.rebuild.enableNg) in your configuration (this will replace the old `nixos-rebuild`), or by adding `nixos-rebuild-ng` to your `environment.systemPackages` (in this case, it will live side-by-side with `nixos-rebuild` as `nixos-rebuild-ng`). It is expected that the next major version of NixOS (25.11) will enable `system.rebuild.enableNg` by default.

- The `nixos-generate-config` command now supports a optional `--flake` option, which will generate a flake.nix file alongside the `configuration.nix` and `hardware-configuration.nix`, providing an easy introduction into flake-based system configurations.

- SSH host key generation has been separated into the dedicated systemd service sshd-keygen.service.

- [`services.dex`](#opt-services.dex.enable) now restarts upon changes to the [`.environmentFile`](#opt-services.dex.environmentFile) option or `path` type entries in `.settings.staticClients[].secretFile`.

- [`services.geoclue2`](#opt-services.geoclue2.enable) now has an `enableStatic` option, which allows the NixOS configuration to specify a fixed location for GeoClue to use.

- [`services.mongodb`](#opt-services.mongodb.enable) is now compatible with the `mongodb-ce` binary package. To make use of it, set [`services.mongodb.package`](#opt-services.mongodb.package) to `pkgs.mongodb-ce`.