Add Rest APIs for Audit data

We need to add a time delta and streaming API to remotely retrieve audit events from a Couchbase Server node,  this is exactally the same interfaces we added for the system event log. 
https://docs.couchbase.com/server/current/rest-api/rest-get-system-events.html 

This is to allow external platforms like a security SIEM, something like Elastic to ingest audit data