maintainers: create sage team

Maintaining all the packages whose updates might break some aspect of
sage.

For reference:
https://github.com/NixOS/nixpkgs/pull/103810#issuecomment-727536510

pkgs/development/libraries/science/math/rubiks/default.nix

@@ -75,7 +75,7 @@ stdenv.mkDerivation rec {
       gpl2 # Michael Reid's and Eric Dietz software
       mit # Dik T. Winter's software
     ];
-    maintainers = with maintainers; [ timokau ];
+    maintainers = teams.sage.members;
     platforms = platforms.unix;
   };
 }