MINOR: Adjust Streams parameter hint on TimeoutException (#6280)

KIP-91 was included in Kafka 2.1.0, so we should mention
`delivery.timeout.ms` in the hint as it's the config that
users would want to change in most cases.

Reviewers: Matthias J. Sax <matthias@confluent.io>, John Roesler <john@confluent.io>, Bill Bejeck <bbejeck@gmail.com>, Guozhang Wang <wangguoz@gmail.com>

streams/src/main/java/org/apache/kafka/streams/processor/internals/RecordCollectorImpl.java

@@ -59,7 +59,9 @@ public class RecordCollectorImpl implements RecordCollector {
         "No more records will be sent and no more offsets will be recorded for this task. " +
         "Enable TRACE logging to view failed record key and value.";
     private final static String EXCEPTION_MESSAGE = "%sAbort sending since %s with a previous record (timestamp %d) to topic %s due to %s";
-    private final static String PARAMETER_HINT = "\nYou can increase producer parameter `retries` and `retry.backoff.ms` to avoid this error.";
+    private final static String PARAMETER_HINT = "\nYou can increase the producer configs `delivery.timeout.ms` and/or " +
+        "`retries` to avoid this error. Note that `retries` is set to infinite by default.";
+
     private volatile KafkaException sendException;
 
     public RecordCollectorImpl(final String streamTaskId,
@@ -125,6 +127,8 @@ public class RecordCollectorImpl implements RecordCollector {
     ) {
         String errorLogMessage = LOG_MESSAGE;
         String errorMessage = EXCEPTION_MESSAGE;
+        // There is no documented API for detecting retriable errors, so we rely on `RetriableException`
+        // even though it's an implementation detail (i.e. we do the best we can given what's available)
         if (exception instanceof RetriableException) {
             errorLogMessage += PARAMETER_HINT;
             errorMessage += PARAMETER_HINT;