[venice] Introduce the Writer operation and clean up the metrics

- introduce a new WriteOp to write directly to Venice
- support AVRO keys for reads and for writes
- remove useless metrics

engine-cli/src/main/java/io/nosqlbench/engine/cli/NBCLI.java

@@ -394,6 +394,7 @@ public class NBCLI implements Function<String[], Integer>, NBLabeledElement {
             if (null != reportGraphiteTo) reporters.addGraphite(reportGraphiteTo, options.wantsMetricsPrefix());
             if (null != options.wantsReportCsvTo())
                 reporters.addCSVReporter(options.wantsReportCsvTo(), options.wantsMetricsPrefix());
+            reporters.addLogger();
             reporters.start(10, options.getReportInterval());
         }