Redis keyspace-events for persistence and replication

Add a keyspace-events control for: 1. RDB re-write completed 2. Configuration file re-written 3. AOF re-write completed

This would allow a companion process to trigger backup operations for the updated files.

Comment From: enjoy-binbin

keyspace-event acts on the keyspace, so i don't think we will support these events. The RDB and AOF one i think now module event can handle it well. and the config file, i am not sure about it, since this issue is old, feel free to open a new to base on the new version so that we can discuss it.