Custom details on payload

Description

Can we add in custom fields with custom information to allow for more details on the message.

What

MessageFactory. has a map called payload, can we do something this?

    Map<String, String> payload = new HashMap<String, String>();
    payload.put("summary", modelData.event().message());
    payload.put("source", "Graylog:" + modelData.event().sourceStreams());
    payload.put("severity", eventPriority);
    payload.put("timestamp", modelData.event().eventTimestamp().toString());
    payload.put("component", "GraylogAlerts");
    payload.put("group", modelData.event().sourceStreams().toString());
    payload.put("class", "alerts");
    payload.put("details", customDetailsMap.toString());

Why

This will help with event alerting