GH-694: Add recordMetadataChannel (send confirm.)

Resolves #694

Also fix deprecation of `ChannelInterceptorAware`.

docs/src/main/asciidoc/overview.adoc

@@ -332,6 +332,16 @@ Set to `true` to override the default binding destination (topic name) with the
 If the header is not present, the default binding destination is used.
 Default: `false`.
 +
+recordMetadataChannel::
+The bean name of a `MessageChannel` to which successful send results should be sent; the bean must exist in the application context.
+The message sent to the channel is the sent message (after conversion, if any) with an additional header `KafkaHeaders.RECORD_METADATA`.
+The header contains a `RecordMetadata` object provided by the Kafka client; it includes the partition and offset where the record was written in the topic.
+
+`ResultMetadata meta = sendResultMsg.getHeaders().get(KafkaHeaders.RECORD_METADATA, RecordMetadata.class)`
+
+Failed sends go the producer error channel (if configured); see <<kafka-error-channels>>.
+Default: null
++
 
 NOTE: The Kafka binder uses the `partitionCount` setting of the producer as a hint to create a topic with the given partition count (in conjunction with the `minPartitionCount`, the maximum of the two being the value being used).
 Exercise caution when configuring both `minPartitionCount` for a binder and `partitionCount` for an application, as the larger value is used.