sysdb: add sysdb_getgrgid_attrs()
sysdb_getgrgid() is the only MPG aware by GID request but only supports
a fixes set of attributes. The new call allows to add additional
arguments.
Related to https://pagure.io/SSSD/sssd/issue/3748
Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>