This adds some basic documentation for the `profile` option in ESQL but
doesn't really explain the results beyond "this is for human debugging."
We're not ready for any kind of specification for this thing, but it is
useful to look at.
This commit adds detailed API docs for the ES|QL async apis, as well as moving the narrative to the ES|QL specific REST docs. Additionally, a few top-level lists are reflowed to reflect that there are now multiple APIs.
* Break out 'Limitations' into separate page
* Add REST API docs
* Restructure commands, functions, and operators refs
* Add placeholder for getting started guide
* Group 'Syntax', 'Metafields', and 'MV fields' under 'Language'
* Add placeholder for Kibana page
* Add link from landing page
* Apply uniform formatting to ACOS, CASE, and DATE_PARSE function refs
* Reword default LIMIT
* Add support for COUNT(*)
* Move 'Commands' and 'Functions and operators' to individual pages
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Co-authored-by: Elastic Machine <elasticmachine@users.noreply.github.com>