Summary

In a nutshell, this PR updates all references to default indices in the APM Server documentation. Here's a detailed list of the changes:

Changes from elastic/beats#20074:

• Renames the "Elastic Cloud" output documentation to "Elasticsearch Service". It updates all terminology and adds tracking links to the ESS product page. It also moves the ESS output documentation to the top of the output list.
• Updates the Elasticsearch output documentation for APM Server. Specifically, it updates the index and indices default pattern for ILM and non-ILM use-cases. (docs: Clarify Elasticsearch output sample config #3870).
• Updates the Elasticsearch output documentation examples for Beats and APM Server. There was a lot of duplication between the ES Output docs and the Secure ES docs. My idea was to simplify the examples in the ES output, and keep all details in Secure ES.

Additional changes:

• Updates Explore data in ES for ILM and non-ILM defaults.
• Removes index name definitions from individual {event_tpye}-indices.asciidoc files.

Related issues

Closes #3870