[SPARK-20874][EXAMPLES] Add Structured Streaming Kafka Source to examples project
[SPARK-20874][EXAMPLES] Add Structured Streaming Kafka Source to examples project

## What changes were proposed in this pull request?

Add Structured Streaming Kafka Source to the `examples` project so that people can run `bin/run-example StructuredKafkaWordCount ...`.

## How was this patch tested?

manually tested it.

Author: Shixiong Zhu <b59cd5ce8cb5ae44d26fc6984be1f84cf74771a7@databricks.com>

Closes #18101 from zsxwing/add-missing-example-dep.

(cherry picked from commit 98c3852986a2cb5f2d249d6c8ef602be283bd90e)
Signed-off-by: Shixiong Zhu <b59cd5ce8cb5ae44d26fc6984be1f84cf74771a7@databricks.com>

apache-spark-on-k8s/spark,publicRoman/spark,jlopezmalla/spark,publicRoman/spark,jlopezmalla/spark,publicRoman/spark,jlopezmalla/spark,apache-spark-on-k8s/spark,publicRoman/spark,apache-spark-on-k8s/spark,jlopezmalla/spark,jlopezmalla/spark,publicRoman/spark,jlopezmalla/spark,publicRoman/spark,apache-spark-on-k8s/spark,apache-spark-on-k8s/spark,apache-spark-on-k8s/spark,jlopezmalla/spark,publicRoman/spark,apache-spark-on-k8s/spark