Add support for Kafka

[joschi]

Add support for Kafka output of the Beats 5.x platform (elastic/beats#942).

https://www.elastic.co/guide/en/beats/filebeat/master/kafka-output.html

[Artemmkin]

@joschi I guess the schema "filebeat -> kafka -> graylog" won't work as of now?

[joschi]

@Artemmkin Correct.

[BenjaminLSmith]

+1

[salekseev]

+1

[CBEPX]

+1