For #2580.

Requires a PR in the Beats repo to persist the changes: elastic/beats#15272.

This PR adds a paragraph to each output page explaining that the es output must be disabled first:

To use this output, edit the {beatname_uc} configuration file to disable the {es}
output by commenting it out...

It also clarifies that for apm-server, Logstash and Kafka enabled defaults to false. This is not the case for beats:

ifndef::apm-server[]
The default value is `true`.
endif::[]
ifdef::apm-server[]
The default value is `false`.
endif::[]

Finally, there is no redis, file, or console section in the .yml configuration files, so I've fixed wording that indicated there was.