[alerting event log] add Kibana server uuid to all logged events

[pmuellr]

Currently we are not setting the Kibana server uuid in the logged events, but should be. This can be done when the event log data is merged down to it's final form, so the clients don't have to add it themselves.

[elasticmachine]

Pinging @elastic/kibana-alerting-services (Team:Alerting Services)