nixos/transmission: adjust settings.umask

* nixos/transmission: change `settings.umask` to be a string

* nixos/transmission: change umask's default value to match the one in
Transmission's documentation

* nixos/doc: add entry for transmission umask option changes

nixos/doc/manual/release-notes/rl-2411.section.md

@@ -448,6 +448,8 @@
   - The `stargazer.allowCgiUser` option has been added, enabling
     Stargazer's `cgi-user` option to work, which was previously broken.
 
+- The type of `services.transmission.settings.umask` has been changed to `str`, and its default value to `"022"`. This was done in accordance with Transmission's documentation. Note that you can't simply wrap the old integer value in a string, you also have to convert it from decimal to octal.
+
 - The `shiori` service now requires an HTTP secret value `SHIORI_HTTP_SECRET_KEY` to be provided via environment variable. The nixos module therefore, now provides an environmentFile option:
 
   ```

nixos/modules/services/torrent/transmission.nix

@@ -133,15 +133,13 @@ in
             description = "Executable to be run at torrent completion.";
           };
           options.umask = mkOption {
-            type = types.int;
-            default = 2;
+            type = types.str;
+            default = "022";
             description = ''
               Sets transmission's file mode creation mask.
               See the umask(2) manpage for more information.
               Users who want their saved torrents to be world-writable
-              may want to set this value to 0.
-              Bear in mind that the json markup language only accepts numbers in base 10,
-              so the standard umask(2) octal notation "022" is written in settings.json as 18.
+              may want to set this value to `000`.
             '';
           };
           options.utp-enabled = mkOption {