fix: page/graph load speed: part 1 (#6611)

* fix: page/graph load speed: part 1
Speed up load_all_os() by caching the full $config['os'] array
Function time goes from 1.13648s -> 0.00073s
The cache is updated during discovery, but only if it is >22hrs old.
Additionally, the cache is not used and a full yaml load is forced if the cache is >24hrs old.
The cache time is controlled by $config['os_def_cache_time'], I don't see any reason anyone would change that time.

* Delete Session.php

* Include the cache directory.

discovery.php

@@ -118,6 +118,8 @@ if (get_lock('schema') === false) {
     require 'includes/sql-schema/update.php';
 }
 
+update_os_cache(); // will only update if needed
+
 $discovered_devices = 0;
 
 if (!empty($config['distributed_poller_group'])) {