title: Does prefetching work with Service Bus Trigger?
body: <p>I have a Durable orchestration client which is Service Bus Topic triggered. </p>
  
  <pre><code>[FunctionName("ServiceBusTrigger")]
          public static async Task ServiceBusTrigger(
              [ServiceBusTrigger("topicname", "subscriptionname", Connection = "MyServiceBusKey")]string mySbMsg,
              [OrchestrationClient]DurableOrchestrationClient starter,
              ILogger log)
          {
              string instanceId = await starter.StartNewAsync("Orchestrator", mySbMsg);
  
              log.LogInformation($"Started orchestration with ID = '{instanceId}'.");
  
          }
  </code></pre>
  
  <p>Does enabling the prefetch count under extensions in <code>host.json</code> cause messages to be prefetched in the Service Bus Trigger?</p>
  
  <p><code>host.json</code>:</p>
  
  <pre><code>{
      "version": "2.0",
      "extensions": {
          "serviceBus": {
              "prefetchCount": 100
          }
      }
  }
  </code></pre>