APM: Put the "reference" back into reference docs

[bmorelli25]

As a prerequisite to the Observability documentation overhaul, we should begin to:

• Separate non-reference content from reference content
• Improve TOC headings to be easier to scan
• Sort lists in a consistent manner (alphabetically)

Beats prereqs

• Make update beats docs docs: Update documentation from Beats apm-server#3459
• Simplify Beats documentation headers (and use consistent wording) [docs] Restructure and refactor beats documentation beats#16825

APM Server work

• Break configuration section into two different sections: Configuration & How to
• Sort lists alphabetically where feasible
• manage storage section is still a mix of reference/guide
• Improve scanability of the TOC by adding shorter nav titles with title abbreviations to APM specific topics:

== Long descriptive page title for SEO
++++
<titleabbrev>Short TOC header</titleabbrev>
++++

Related Issues

• Beats Reference content: Let's put the "reference" back into reference docs beats#16821
• Beats restructure and refactor: [docs] Restructure and refactor beats documentation beats#16825

[bmorelli25]

I moved this to obs-docs to track additional changes, but for the most part, this issue was completed in elastic/apm-server#3459 and elastic/beats#16825.

The more I think about it, I think it makes more sense to close this and track additional changes in https://github.com/elastic/observability-dev/issues/647.