[QUERY] In azure-messaging-eventhubs, what's the Track2 equivalent for storing partition checkpoint on partition close

## Context
In Track1, we can save the partition context on partition close by:
```java
@Override
public void onClose(PartitionContext partitionContext, CloseReason closeReason) throws Exception{
partitionContext.checkpoint();
closeCallback.invoke(Done.getInstance());
}
```

In Track2, we only have
```java
public EventProcessorClientBuilder processPartitionClose(Consumer closePartition) {
this.processPartitionClose = closePartition;
return this;
}
```
And there's no `checkpiont()` method in [PartitionContext](https://github.com/Azure/azure-sdk-for-java/blob/main/sdk/eventhubs/azure-messaging-eventhubs/src/main/java/com/azure/messaging/eventhubs/models/PartitionContext.java#L13) to store partition checkpoint anymore.

## Question
Is the removal of this "checkpoint on partition close" behavior in Track2 intended? If so, we should explicitly call this out in migration guide.