Expand/fix custom presets docs

[kilfoyle]

This PR updates the performance tuning presets sections of the Elasticsearch output docs:

• Updates some of the setting terms (e.g., compression to compression_level
• Adds detail about customizing settings.

Rel: #869

Please see these example preview pages:

• Fleet-managed Elasticsearch output
• Standalone agent Elasticsearch output memory queue settings

Here's the updated section:

[github-actions]

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[kpollich]

These need the queue.mem. prefix per elastic/kibana#175892

[kilfoyle]

Thanks @kpollich. I've pushed the change here and at line 231 below.

I'm a bit confused though. Would you know if these settings descriptions for standalone agent also need to be updated? We have queue memory settings described for Elasticsearch, Logstash, and Kafka (currently in an open PR).

Those pages all show an example configuration like this:

queue.mem:
  events: 4096
  flush.min_events: 512
  flush.timeout: 5s

[kpollich]

The "expanded" YAML syntax is equivalent, but perhaps we should be consistent, e.g.

queue.mem.events: 4096
queue.mem.flush.min_events: 512
queue.mem.flush.timeout: 5s

is equivalent to

queue:
  mem:
    events: 4096
    flush:
      min_events: 512
      timeout: 5s

which is also equivalent to

queue.mem:
  events: 4096
  flush.min_events: 512
  flush.timeout: 5s

In YAML, dot notation or indent notation are both valid. It's largely subjective where one uses dots and where one introduces a new level of indentation. I'm in favor of aligning these example code blocks with what's in those other preexisting docs if only because it'd be less work than updating those other docs to match the way we have it in these ingest docs 🙂

[kilfoyle]

Brilliiant! Thanks @kpollich for the super clear explanation. I wasn't sure and certainly didn't want to just guess. :-)

I've updated all instances of the events, flush.min_events, and flush.timeout settings to be queue.mem.events, queue.mem.flush.min_events, and queue.mem.flush.timeout, respectively.

The configuration examples in the standalone agent output settings docs are now like this:

  queue.mem.events: 4096
  queue.mem.flush.min_events: 512
  queue.mem.flush.timeout: 5s

The docs preview linked in the description will update once the CI checks have re-run.

[kpollich]

🚀 Awesome work as always