Time-series docs changes (#135613)

* Extend rate documentation

* [CI] Auto commit changes from spotless

* add link in stats

* add link in stats

* Update stats-by.md

* fix link

* fix preview

* [CI] Auto commit changes from spotless

* fix preview

* fix preview

* fix preview

* Apply suggestions from code review

Co-authored-by: Liam Thompson <[email protected]>

* update from comments

* mark time series aggs as preview

* [CI] Auto commit changes from spotless

* Update stats-by.md

* Update docs/reference/query-languages/esql/_snippets/commands/layout/stats-by.md

Co-authored-by: Felix Barnsteiner <[email protected]>

* fix from comment

* gen files for rate

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Co-authored-by: elasticsearchmachine <[email protected]>
Co-authored-by: Liam Thompson <[email protected]>
Co-authored-by: Felix Barnsteiner <[email protected]>

Author: 4 people