Minor Description
Add metrics for Elasticsearch producers. For now, we'll only track success events (number of successful bulk sends, number of documents inserted, and number of documents updated). Since the current ES producer fails the job when ES returns an error, there's no benefit yet to tracking negative events because Samza does not seem to flush metrics before shutting down (at least when I tested with ThreadJob).
I've implemented metrics here (https://github.com/Quantiply/rico/tree/master/samza-elasticsearch/src/main/java/org/apache/samza/system/elasticsearch) and will work on creating a patch.