Add groups to directory sync user struct

[bmanifold]

In looking through the WorkOS API docs, I noticed the response for directory sync users included groups nested within the user data. When attempting to use the workos-elixir package I ran in to an issue where I needed the group information for a user, however it wasn't part of the user struct.

This PR adds the groups info to the directory sync user struct.

Thank you for considering this PR and please let me know if I need to change/add anything.