configure.ac: detect extended NSS API provided by SSSD
SSSD exposes an extended NSS API via libsss_nss_idmap. This API allows
to query getpwnam()/getgrnam()/getgruid()/getpwuid()/getgrouplist()
information with a timeout per request. As result, an application has
possibility to cancel too long request.
This API also allows to ignore SSSD cache or invalidate it when
requesting certain information. slapi-nis needs this functionality when
invalidating own entries as result of changes done by other LDAP clients
in the areas which slapi-nis doesn't track directly.
For example, an update of ID override in the Default Trust View should
invalidate user or group entry for that AD object. Since retrieval of
the user/group information relies on SSSD, SSSD needs to be notified
that there is a change in ID override and evict the entry from its cache
as well.