Support for compute sinks

[javierluraschi]

Foreach sink - Runs arbitrary computation on the records in the output. See later in the section for more details.

https://spark.apache.org/docs/latest/structured-streaming-programming-guide.html#output-sinks

[harryprince]

spark streaming is very meaningful for the online anti-spam machine learning scenario, wish to see better streaming pipeline support from Kafka reading to HBase writing.