Doc: Rethink plan to reorganize settings docs

[karenzone]

The same settings are documented in different places originating from different source files. (See queue settings, for example.) This situation sets us up for documentation getting out of sync because a setting gets updated in one place but not another.

Consider a single-sourcing approach that defines settings (as attributes perhaps) in one file to facilitate reuse wherever we need them.

ToDo: Add documentation about the interaction of overlapping settings in logstash.yml, pipelines.yml, and central management.

See also: #13419

[karenzone]

Notes to self @karenzone:

• Think about setting up each setting as an attribute using the definition list format.

• Possible format for content:

  ``queue.max_bytes`:: The total capacity of _each queue_ in number of bytes. 
  Unless overridden in `pipelines.yml` or central management, each persistent
  queue will be sized at the value of `queue.max_bytes` specified in
  `logstash.yml`. 
  The default is 1024mb (1gb).
  

  

• This project would also be an opportunity to add notes about the interaction of overlapping settings in logstash.yml, pipelines.yml, and central management.

ToDo:

• Test to be sure that we could expand content (with +) and keep it inline for situations where additional information is needed. (Tips, notes, etc.)

[karenzone]

Note to self @karenzone: When adding new attributes and content, review carefully to be sure that no content is dropped because of bad formatting, returns, etc.

[karenzone]

Moved to HOLD because of competing priorities

[karenzone]

This work was started in https://github.com/elastic/logstash/pull/14384 before it was put on hold. When I pick this up again, I will use the work started in #14384, but implement it as a series of smaller, more granular PRs.

TO DO: Divide work into chunks and track in a meta issue.