This implements `INLINESTATS`. Most of the heavy lifting is done by
`LOOKUP`, with this change mostly adding a new abstraction to logical
plans, and interface I'm calling `Phased`. Implementing this interface
allows a logical plan node to cut the query into phases. `INLINESTATS`
implements it by asking for a "first phase" that's the same query, up to
`INLINESTATS`, but with `INLINESTATS` replaced with `STATS`. The next
phase replaces the `INLINESTATS` with a `LOOKUP` on the results of the
first phase.
So, this query:
```
FROM foo
| EVAL bar = a * b
| INLINESTATS m = MAX(bar) BY b
| WHERE m = bar
| LIMIT 1
```
gets split into
```
FROM foo
| EVAL bar = a * b
| STATS m = MAX(bar) BY b
```
followed by
```
FROM foo
| EVAL bar = a * b
| LOOKUP (results of m = MAX(bar) BY b) ON b
| WHERE m = bar
| LIMIT 1
```
* Page structure
* More getting started content
* Fix build errors
* Small improvements
* Typo
* Add link to public demo environment
* Review feedback
* Update docs/reference/esql/esql-get-started.asciidoc
Co-authored-by: Andrei Stefan <astefan@users.noreply.github.com>
* Review feedback
---------
Co-authored-by: Andrei Stefan <astefan@users.noreply.github.com>
* 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
---------
Co-authored-by: Elastic Machine <elasticmachine@users.noreply.github.com>
