Docs unclear that metadata is opt-in

[yaauie]

The separate call-out on metadata fields fails to call out that metadata will only be added if decorate_events is set to true; this leads to confusion and frustration.

[ghost]

On a related subject, the description of decorate_events suggests it will add a field to the event called kafka, not a field within the metadata.

[ahammani]

Many thanks @yaauie you solved my issue.

Indeed the metadata paragraph should talk about decorate_events

[synhershko]

Fixed by #296

[nephel]

A far as I can see, the documentation still does not contain the following line
Metadata is only added to the event if the decorate_events option is set to true (it defaults to false).

is still missing from the current docs https://www.elastic.co/guide/en/logstash/7.1/plugins-inputs-kafka.html

Looks like the PR #296 failed