docs: pipeline: outputs: kafka: Fixed missing parameter.

  Applies to #2294

Signed-off-by: Eric D. Schabell <eric@schabell.org>

Author: eschabell

pipeline/outputs/kafka.md

@@ -303,7 +303,7 @@ pipeline:
   Match    *
   Brokers  b-1.mycluster.kafka.us-east-1.amazonaws.com:9098
   Topics   my-topic
-```
+  rdkafka.sasl.mechanism aws_msk_iam
 
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