code: public GitlabGroupMember addGroupMember(GitlabGroup group, GitlabUser user, GitlabAccessLevel accessLevel) throws IOException {
          return addGroupMember(group.getId(), user.getId(), accessLevel);
      }
docs: Add a group member.
  
  @param group       the GitlabGroup
  @param user        the GitlabUser
  @param accessLevel the GitlabAccessLevel
  @return the GitlabGroupMember
  @throws IOException on gitlab api call error