Add stat to track pages queued for eviction after LRU sorting

Eviction server goes through the process of finding pages that are evictable, sort them based on when these pages were last accessed and then based on a certain logic might discard a portion of these pages to approximate the LRU scheme. pages queued for eviction statistic accounts for the count of initial evictable pages before the sorting. At the moment there is no statistic to tell what number of pages were actually put into the eviction queue. This ticket is to add a new statistic.