[APM] docs: restructure APM documentation for 7.7

[bmorelli25]

Summary

This PR:

• Separates non-reference content from reference content to create a triage location for guide content as we adapt what we have into how-to guides, and begin to create more task-focussed documentation.
• Improves the TOC structure and headings by moving content from the "Using APM" bucket, and making use of table abbreviations to simplify the TOC headings.

In addition, this PR:

• Explains where supported configurations for central config are documented
• Updates service map documentation with feedback from @nehaduggal

Reviewers: Please visit the doc preview link and click around. Any feedback on the new structure is welcome.

Doc preview

http://kibana_63280.docs-preview.app.elstc.co/guide/en/kibana/master/xpack-apm.html
https://www.elastic.co/guide/en/kibana/current/xpack-apm.html

Screenshots

This is the proposed content structure:

collapsed

expanded

Related Issues

Closes #60462.
Closes elastic/apm#232.
Closes #63510.
Closes #63475.

[elasticmachine]

Pinging @elastic/apm-ui (Team:apm)

[bmorelli25]

@nehaduggal See https://github.com/elastic/kibana/pull/63280/files#diff-369bdd3f2877c4bfb5c34e738980fc81 for service map updates

[bmorelli25]

I need to fix a link in the APM Overview before the docs preview will work.

12:47:14 INFO:build_docs:Bad cross-document links:
12:47:14 INFO:build_docs:  /tmp/docsbuild/target_repo/html/en/apm/get-started/master/components.html:
12:47:14 INFO:build_docs:   - en/kibana/master/apm-bottlenecks.html

EDIT: Links updated in elastic/apm-server#3643.

[nehaduggal]

Added a few comments.

[nehaduggal]

"or is unable to propagate a traceparent header" Because you can see external service and database calls and won't see things like load balancers because they themselves don't explicitly propagate the traceparent header. Maybe we can specify what things can't propagate headers explicitly - e.g. load balancers, databases, message queues.

[bmorelli25]

@elasticmachine, run elasticsearch-ci/docs

[bmorelli25]

@elasticmachine, run elasticsearch-ci/docs

[bmorelli25]

Based on feedback from @nehaduggal , I’ve made the following additional changes:

• PR feedback
• Defined traces in traces.asciidoc and getting-started.asciidoc
• Moved deployment annotations to how-to section
• Renamed “advanced queries” to “query your data"
• Added an example to the “query your data” page, and reworked content
• Improved APM settings description and added links to index details in the APM Server reference

Other changes:

• More clean up
• Moves watcher error reports to how-to section

To do / questions:

• Explain how to enable ML in machine-learning-integration.html
• Need to figure out what to do with the distributed tracing content in traces.asciidoc. This is really just copied over information from the APM Overview, and it wouldn’t even be necessary if all of our documentation lived in one place. I wonder if we can turn it into task based and move it into the how-to section. Something like, “Visualize distributed traces”, and talk about the span waterfall and service maps

[dgieselaar]

Great work Brandon - one suggestion about alert tags that I should have given earlier, but other than LGTM

[bmorelli25]

Taking care of #63510 in this PR since I already have it open. See 4594da6.

[bmorelli25]

Added #63475 in ad3c5f3. Still need to confirm the accuracy of the list.