When using EventHubOutput with EventData any Properties added to the EventData are NOT propagated to the Message on EventHub

[cicorias]

Description

Using EventHubOutput on a function that returns a type of EventData results in loss of the Properties that should be propagated to the EventHub message.

Using EventHubOutput

Using non Azure Functions via console app as follows:

           var eventData = new EventData(Encoding.UTF8.GetBytes($"Event {i}"));
            eventData.Properties.Add("EventId", i);
            eventData.Properties.Add("EventType", "Test");
            eventData.Properties.Add("EventTime", DateTime.UtcNow);
            await producerClient.SendAsync(new [] {eventData}, sendOptions);

Steps to reproduce

1. Create an azure function of any Trigger type with EventHubOutput return type of EventData or EventData[]

[EventHubOutput("ns1", Connection = "APP_TARGET_EVENT_HUB")]
   public EventData Run(
       [EventGridTrigger] EventGridEvent resultEvent,
       FunctionContext context)
   ...

2. In the body create an EventData instance with properties.

        var outEvent = new EventData(Encoding.UTF8.GetBytes(JsonSerializer.Serialize(defenderScanResult))){
            Properties = {
                { "source", "FOO" },
                { "thing", "iotevent" }
            }
        };

       return outEvent;

3. Using Service bus explorer or any other method listen to the Event Hub and examine the message

NOTE: on the event received there will be no Properties propagated except for Diagnostic-Id