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/m4ri/default.nix

@@ -24,7 +24,7 @@ stdenv.mkDerivation rec {
     homepage = "https://malb.bitbucket.io/m4ri/";
     description = "Library to do fast arithmetic with dense matrices over F_2";
     license = licenses.gpl2Plus;
-    maintainers = with maintainers; [ timokau ];
+    maintainers = teams.sage.members;
     platforms = platforms.unix;
   };
 }