[Event Hubs] Fix enumerable send (#30370)

The focus of these changes is to fix a bug in the `SendAsync` overload that
accepts and enumerable where the partition key is ignored.

Author: jsquire

sdk/eventhub/Azure.Messaging.EventHubs.Processor/CHANGELOG.md

@@ -2,14 +2,16 @@
 
 ## 5.8.0-beta.1 (Unreleased)
 
-### Features Added
+### Acknowledgments
 
-### Breaking Changes
+Thank you to our developer community members who helped to make the Event Hubs client libraries better with their contributions to this release:
 
-### Bugs Fixed
+- Daniel Marbach _([GitHub](https://github.com/danielmarbach))_
 
 ### Other Changes
 
+- Miscellaneous performance improvements by reducing memory allocations. _(A community contribution, courtesy of [danielmarbach](https://github.com/danielmarbach))_
+
 ## 5.7.1 (2022-07-07)
 
 ### Acknowledgments

sdk/eventhub/Azure.Messaging.EventHubs/CHANGELOG.md

@@ -8,12 +8,10 @@ Thank you to our developer community members who helped to make the Event Hubs c
 
 - Daniel Marbach _([GitHub](https://github.com/danielmarbach))_
 
-### Features Added
-
-### Breaking Changes
-
 ### Bugs Fixed
 
+- Fixed a regression with the `EventHubProducerClient` overloads of `SendAsync` which accept an enumerable of events.  When specifying a partition key, it was ignored when sending.  As a result, the Event Hub applied round-robin partition assignment, spreading events across partitions rather than grouping them in a single partition.
+
 ### Other Changes
 
 - Reduced memory allocations when converting messages into the underlying AMQP primitives. _(A community contribution, courtesy of [danielmarbach](https://github.com/danielmarbach))_

sdk/eventhub/Azure.Messaging.EventHubs/src/Amqp/AmqpProducer.cs

@@ -479,7 +479,7 @@ protected virtual async Task SendAsync(IReadOnlyCollection<AmqpMessage> messages
 
                     try
                     {
-                        using AmqpMessage batchMessage = MessageConverter.CreateBatchFromMessages(messages);
+                        using AmqpMessage batchMessage = MessageConverter.CreateBatchFromMessages(messages, partitionKey);
 
                         if (!SendLink.TryGetOpenedObject(out link))
                         {