Configure auto discard sleeping tabs

Setting this policy enables inactive (sleeping) tabs to be automatically discarded after 1.5 days of inactivity. This is done to save memory. When the user switches back to a discarded tab, the tab needs to be reloaded. If the 'SleepingTabsEnabled' (Configure sleeping tabs) policy is enabled, then this feature is enabled by default. If the 'SleepingTabsEnabled' is disabled, then this feature is disabled by default and can't be enabled. If enabled, idle background tabs will be discarded after 1.5 days. If disabled, idle background tab won't be discarded after 1.5 days. Tabs can still be discarded for other reasons if this policy is disabled.