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/python-modules/flask-silk/default.nix

@@ -24,7 +24,7 @@ buildPythonPackage {
   meta = with stdenv.lib; {
     description = "Adds silk icons to your Flask application or module, or extension";
     license = licenses.bsd3;
-    maintainers = with maintainers; [ timokau ];
+    maintainers = teams.sage.members;
     homepage = "https://github.com/sublee/flask-silk";
   };
 }