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/applications/science/math/symmetrica/default.nix

@@ -29,7 +29,7 @@ stdenv.mkDerivation rec {
   meta = with lib; {
     description = ''A collection of routines for representation theory and combinatorics'';
     license = licenses.isc;
-    maintainers = with maintainers; [raskin timokau];
+    maintainers = with maintainers; [raskin] ++ teams.sage.members;
     platforms = platforms.unix;
     homepage = "https://gitlab.com/sagemath/symmetrica";
   };