nixos/nextcloud: update docs

* Update related packages for pkg option.
* Add release notes.

nixos/doc/manual/release-notes/rl-2505.section.md

@@ -184,6 +184,14 @@
 - `binwalk` was updated to 3.1.0, which has been rewritten in rust. The python module is no longer available.
   See the release notes of [3.1.0](https://github.com/ReFirmLabs/binwalk/releases/tag/v3.1.0) for more information.
 
+- The latest available version of Nextcloud is v31 (available as `pkgs.nextcloud31`). The installation logic is as follows:
+  - If [`services.nextcloud.package`](#opt-services.nextcloud.package) is specified explicitly, this package will be installed (**recommended**)
+  - If [`system.stateVersion`](#opt-system.stateVersion) is >=24.11, `pkgs.nextcloud30` will be installed by default.
+  - If [`system.stateVersion`](#opt-system.stateVersion) is >=24.05, `pkgs.nextcloud31` will be installed by default.
+  - Please note that an upgrade from v29 (or older) to v31 directly is not possible. Please upgrade to `nextcloud30` (or earlier) first. Nextcloud prohibits skipping major versions while upgrading. You can upgrade by declaring [`services.nextcloud.package = pkgs.nextcloud30;`](options.html#opt-services.nextcloud.package).
+
+- `pkgs.nextcloud28` has been removed since it's out of support upstream.
+
 - `buildGoModule` now passes environment variables via the `env` attribute. `CGO_ENABLED` should now be specified with `env.CGO_ENABLED` when passing to buildGoModule. Direct specification of `CGO_ENABLED` is now redirected by a compatibility layer with a warning, but will become an error in future releases.
 
   Go-related environment variables previously shadowed by `buildGoModule` now results in errors when specified directly. Such variables include `GOOS` and `GOARCH`.

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

@@ -303,7 +303,7 @@ in {
     package = mkOption {
       type = types.package;
       description = "Which package to use for the Nextcloud instance.";
-      relatedPackages = [ "nextcloud29" "nextcloud30" ];
+      relatedPackages = [ "nextcloud29" "nextcloud30" "nextcloud31" ];
     };
     phpPackage = mkPackageOption pkgs "php" {
       example = "php82";