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/arb/default.nix

@@ -21,7 +21,7 @@ stdenv.mkDerivation rec {
     description = ''A library for arbitrary-precision interval arithmetic'';
     homepage = "http://arblib.org/";
     license = stdenv.lib.licenses.lgpl21Plus;
-    maintainers = with maintainers; [ raskin timokau ];
+    maintainers = with maintainers; [ raskin ] ++ teams.sage.members;
     platforms = stdenv.lib.platforms.unix;
   };
 }