Deduplicate event ids

Redfish specification states:
```
The value of the id field shall be the same as the Id property in the
event payload. The value of the Id property in the event payload should

Deduplicate event ids

Redfish specification states:
```
The value of the id field shall be the same as the Id property in the
event payload. The value of the Id property in the event payload should
be the same as the EventId property of the last event record in the
Events array. The value of the EventId property for an event record
should be a positive integer value and should be generated in a
sequential manner.
```

The event service code did not implement that correctly. So:
1. Add ID fields for all events.
2. Remove the per-sse connection id field and rely solely on
EventServiceManager.
3. Make sure all paths, (including metric report) are generating an
event id that's based on the eventservice event id

Tested: Redfish event listener now sees events populated.
LastEventId when sent to the SSE socket now sees a contiguous id.

```
uri=$(curl -s --user "root:0penBmc" -k "https://192.168.7.2/redfish/v1/EventService" | jq -r .ServerSentEventUri)
curl -u root:0penBmc -vvv -k -N -H "Accept: text/event-stream" -H "Last-Event-Id: 0" "https://192.168.7.2$uri"
```

Change-Id: Ic32e036f40a53a9b2715639ae384d7891c768260
Signed-off-by: Ed Tanous <etanous@nvidia.com>

show more ...

Unit test: event_log.cpp

Provide basic unit test coverage for the functions from event_log.cpp.

Tested: Unit tests pass.

Change-Id: Ib555d2404e0f5cc5d5610d466100d0f07c79f5d9
Signed-off-by: Alexand

Unit test: event_log.cpp

Provide basic unit test coverage for the functions from event_log.cpp.

Tested: Unit tests pass.

Change-Id: Ib555d2404e0f5cc5d5610d466100d0f07c79f5d9
Signed-off-by: Alexander Hansen <alexander.hansen@9elements.com>

show more ...