SSSD cache update performance improvement
Previously, the System Security Services Daemon (SSSD) always updated all cached entries after the cache validity timeout passed. This consumed unnecessarily resources on the client and the server, for entries that have not been changed. SSSD has been enhanced and now checks if the cached entry requires an update. The time stamp values are increased for unchanged entries and stored in the new SSSD database `/var/lib/sss/db/timestamps_$domain.ldb`. This enhancement improves the performance for entries that rarely change on the server side, such as groups.