Fix APM ES output docs incorrectly labeled as not applicable to Fleet-managed APM

[Copilot]

Fixes #elastic/apm-server#18937

The APM Elasticsearch output configuration documentation incorrectly stated that it "only applies to APM Server binary users" and redirected Fleet-managed users to the generic Fleet Elasticsearch output documentation. This was misleading because:

1. The APM-specific Elasticsearch configuration options described in the documentation do apply to both standalone and Fleet-managed APM Server
2. Fleet-managed users need to configure these same APM-specific settings (not the generic Fleet ES output settings) through the Fleet UI in Kibana
3. Only the YAML configuration method is specific to binary users

Before this change:

This documentation only applies to APM Server binary users. Fleet-managed users should see Configure the {{es}} output.

After this change:

The configuration options described in this documentation apply to both APM Server binary and Fleet-managed APM Server. However, the YAML configuration method shown here only applies to APM Server binary users. Fleet-managed users configure these same APM-specific Elasticsearch output settings through the Fleet UI in Kibana.

This change ensures Fleet-managed APM users understand they can use the configuration options documented here, but should configure them via the Fleet UI rather than being incorrectly directed to unrelated Fleet ES output documentation.

Original prompt

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This section details on the original issue you should resolve

<issue_title>[Internal]: APM ES config incorrectly labeled as not applicable to fleet-managed APM</issue_title>
<issue_description>### Description

Mirrors issue elastic/apm-server#18937

In https://www.elastic.co/docs/solutions/observability/apm/apm-server/configure-elasticsearch-output ,

This documentation only applies to APM Server binary users. Fleet-managed users should see Configure the Elasticsearch output.

but this is not accurate. The ES configs listed in APM ES output docs are applicable to both standalone and fleet-managed, but the way to configure them through yaml is specific to standalone. Fleet-managed APM needs to configure the APM ES output configs (not Fleet ES output configs) via fleet UI

Resources

https://www.elastic.co/docs/solutions/observability/apm/apm-server/configure-elasticsearch-output

Which documentation set does this change impact?

Elastic On-Prem and Cloud (all)

Feature differences

Applies to both on-prem and cloud

What release is this request related to?

9.2

Serverless release

NA

Collaboration model

The documentation team

Point of contact.

Main contact: @carsonip

Stakeholders:
</issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes #3342

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[carsonip]

isn't this a duplicate of #3343 ?