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/rankwidth/default.nix

@@ -21,7 +21,7 @@ stdenv.mkDerivation rec {
   meta = with stdenv.lib; {
     description = "Calculates rank-width and rank-decompositions";
     license = with licenses; [ gpl2Plus ];
-    maintainers = with maintainers; [ timokau ];
+    maintainers = teams.sage.members;
     platforms = platforms.unix;
   };
 }