* Returns a response entity containing a list of UserGroupAsso objects related to the given groupId.
* If no user-group associations are found for the given groupId, a not-found response entity is returned.
*
* @param groupId the ID of the group to retrieve user-group associations for
* @return a response entity containing a list of UserGroupAsso objects related to the given groupId, or a not-found response entity if no associations are found