Port/leverage weave event to CHIP in data model

[yunhanw-google]

@mrjerryjohns has presented weave event spec in TSG data model team, and received the broad agreement on it. I am working on the initial porting, leverage and prototype for event on CHIP.

Eventing: Motivation
--A way to provide a historical record/log of notable ‘happenings’
--Capture every single ‘edge’ / change
--Send it reliably to interested observers
--Can contain rich metadata

For the existing zcl, there exists 3 gaps
Gap 1: Inconsistent queuing semantics with attribute reporting
--Different queuing constructs observed between ZCL clusters

Gap 2: Lack of meta-model construct to be able to define events
--ZCL today defines in two ways:
Circular ‘tables’ in attributes
‘Notification’ Commands
Need a better construct

Gap 3: Protocol mapping is inefficient, not scalable
--No durable ID per event
--No batching
--No timestamps

We will leverage weave event implementation, create new meta-model construct for Events:
All events have:
Cluster ID + Event Type ID
64-bit unique ID for each event instance, monotonically vended
Importance Levels
Timestamp (system time OR wall-time)

We will modify Reporting protocol to support shuttling batched Events as well
Custom interest set for events
Batched payloads
Synchronization
Event ID optimization