The event data.
The timestamp of the event.
aws.evidently.evaluation specifies an evaluation event, which determines
which feature variation that a user sees. aws.evidently.custom specifies a custom
event, which generates metrics from user actions such as clicks and checkouts.
A structure that contains the information about one evaluation event or custom event sent to Evidently. This is a JSON payload. If this event specifies a pre-defined event type, the payload must follow the defined event schema.