nixos/install-tools: Add manpages to packages instead of seperating them

Since each such `nixos-*` tool has it's own derivation, exposed in pkgs,
There is no point in separating the manuals from the packages. If
someone wishes to have the tools without the manuals, they can use
meta.outputsToInstall to disable the installation of the manpages of
these packages. This Fixes #244450.

nixos/modules/misc/documentation.nix

@@ -346,7 +346,7 @@ in
       system.build.manual = manual;
 
       environment.systemPackages = []
-        ++ optional cfg.man.enable manual.manpages
+        ++ optional cfg.man.enable manual.configuration-manual
         ++ optionals cfg.doc.enable [ manual.manualHTML nixos-help ];
     })