Begins adding support for running "tagged queries" to the compute
engine. Here, it's just the `LuceneSourceOperator` because that's
useful and contained.
Example time! Say you are running:
```
FROM foo
| STATS MAX(v) BY ROUND_TO(g, 0, 100, 1000, 100000)
```
It's *often* faster to run this as four queries:
* The docs that round to `0`
* The docs that round to `100`
* The docs that round to `1000`
* The docs that round to `100000`
This creates an ESQL operator that can run these queries, one after the
other and attach those tags.
Aggs uses this trick and it's *way* faster when it can push down count
queries, but it's still faster when it pushes doc loading things. This
implementation in `LuceneSourceOperator` is quite similar to the doc
loading version in _search.
I don't have performance measurements yet because I haven't plugged this
into the language. In _search we call this `filter-by-filter` and enable
it when each group averages to more than 5000 documents and when there
isn't an `_doc_count` field. It's faster in those cases not to push. I
expect we'll be pretty similar.
Documents that the VALUES aggregate function returns unique documents
and points folks to the TOP aggregate function if they want to keep
dupes.
Closes#128091
---------
Co-authored-by: Liam Thompson <32779855+leemthompo@users.noreply.github.com>
Building on the work started in https://github.com/elastic/elasticsearch/pull/123904, we now want to auto-generate most of the small subfiles from the ES|QL functions unit tests.
This work also investigates any remaining discrepancies between the original asciidoc version and the new markdown, and tries to minimize differences so the docs do not look too different.
The kibana json and markdown files are moved to a new location, and the operator docs are a little more generated than before (although still largely manual).
