Add Kafka to osquerybeat+endpoint spec files. (#3153)

What the summary says, all of the libbeat based spec files already
declare that they support Kafka (which would have only worked for
standalone agents). Needed to unblock integration testing of Kafka
support for Fleet managed agents.

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

Author: cmacknz

specs/endpoint-security.spec.yml

@@ -10,6 +10,7 @@ inputs:
     outputs:
       - elasticsearch
       - logstash
+      - kafka
     proxied_actions:
       - UNENROLL
       - UPGRADE

specs/osquerybeat.spec.yml

@@ -13,6 +13,7 @@ inputs:
     outputs:
       - elasticsearch
       - logstash
+      - kafka
     command:
       restart_monitoring_period: 5s
       maximum_restarts_per_period: 1