This PR adds detailed documentation for `logsdb` mode, covering several key aspects of its default behavior and configuration options.
It includes:
- default settings for index sorting (`index.sort.field`, `index.sort.order`, etc.).
- usage of synthetic `_source` by default.
- information about specialized codecs and how users can override them.
- default behavior for `ignore_malformed` and `ignore_above` settings, including precedence rules.
- explanation of how fields without `doc_values` are handled and what we do if they are missing.
This adds minimal docs around how to the new logs index mode for data
streams (most common use case). This is minimal because logs index mode
is still in tech preview. Minimal docs should allow any interested users
to experiment with the new logs index mode.