MINOR: Default to 5 partitions of the __consumer_offsets topic in Streams integration tests (#7331)

Given that the tests do not create clusters larger than 3, we do not gain much by creating 50 partitions for that topic. Reducing it should slightly increase test startup and shutdown speed.

Reviewers: Matthias J. Sax <mjsax@apache.org>, Guozhang Wang <wangguoz@gmail.com>, Bill Bejeck <bbejeck@gmail.com>

streams/src/test/java/org/apache/kafka/streams/integration/utils/EmbeddedKafkaCluster.java

@@ -94,6 +94,7 @@ public class EmbeddedKafkaCluster extends ExternalResource {
         putIfAbsent(brokerConfig, KafkaConfig$.MODULE$.GroupMinSessionTimeoutMsProp(), 0);
         putIfAbsent(brokerConfig, KafkaConfig$.MODULE$.GroupInitialRebalanceDelayMsProp(), 0);
         putIfAbsent(brokerConfig, KafkaConfig$.MODULE$.OffsetsTopicReplicationFactorProp(), (short) 1);
+        putIfAbsent(brokerConfig, KafkaConfig$.MODULE$.OffsetsTopicPartitionsProp(), 5);
         putIfAbsent(brokerConfig, KafkaConfig$.MODULE$.AutoCreateTopicsEnableProp(), true);
 
         for (int i = 0; i < brokers.length; i++) {