refreshing the auto-discovered policy based on events seen on that policy

[nyrahul]

Currently, the engine checks if there are any rules that are changed in the auto-discovered policy and only in that case updates the policies with the changes.

However, we want the ability for the user to know if there were any recent events for the auto-discovered policy. User can then should be able to say, "I want to delete the auto-discovered policies that haven't seen any activity/events in the past two months".

From the implementation PoV, we need to keep a timestamp which gets updated whenever an event is received on the given discovered policy. This would result in more updates to the DB but the updates are only for the timestamps and thus minimal.