Enable asynchronous message send for kafka producer

Kafka-events plugin supports asynchronous message send. Setup local
environments to reflect production settings.

Feature: Issue 12604
Change-Id: I53c567e34a74dbcd88365c8a8c616829aa3175b4

setup_local_env/configs/gerrit.config

diff --git a/setup_local_env/configs/gerrit.config b/setup_local_env/configs/gerrit.config
index 6f49cd7..f9eca89 100644
--- a/setup_local_env/configs/gerrit.config
+++ b/setup_local_env/configs/gerrit.config
@@ -40,6 +40,7 @@
 [plugin "websession-flatfile"]
     directory = $FAKE_NFS
 [plugin "kafka-events"]
+    sendAsync = true
     bootstrapServers = localhost:$KAFKA_PORT
     groupId = $KAFKA_GROUP_ID
     numberOfSubscribers = 6