Add initial key expiry handling to monitoring.lua

A function, set_initial_expiry, has been introduced to handle initial expiry time for a given redis key in the monitoring.lua file. This function gets called when a new session is established. Additionally, the expiry time for redis keys in callback.lua has been reduced from 24 hours (86400 seconds) to 1 hour (3600 seconds).

Signed-off-by: Christian Roessner c@roessner.co