[kafka] Add missing event.* fields into ecs.yml

[kaiyan-sheng]

What does this PR do?

This PR is to add missing event.* fields into ecs.yml for Kafka integration.

closes #2782

[elasticmachine]

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• Start Time: 2022-03-08T17:24:16.735+0000

• Duration: 12 min 57 sec

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