Expected JSON format - timestamp

[kklopfenstein]

It looks like if log events are in JSON format, cwlogs expects the JSON to be structured in this format:

type Event struct {
	Level   Level     `json:"level"`
	Time    time.Time `json:"time"`
	Info    EventInfo `json:"info"`
	Data    EventData `json:"data"`
	Message string    `json:"message"`
}

https://github.com/segmentio/ecs-logs-go/blob/46096d8f38d354840bbc51bf2d425416a907dd6b/event.go#L63

Our project outputs logs with a timeMillis epoch value and it took a while to get to the bottom of why the time was displaying incorrectly.

Does documentation exist somewhere on this event format? Also, I think that the timestamp should be populated for the event based on the AWS event timestamp if the json timestamp isn't found.