Introduce an optional k param for knn query
If k is not set, knn query has the previous behaviour:
- `num_candidates` docs is collected from each shard. This `num_candidates` docs
are used for combining with results with other queries and aggregations on each shard.
- docs from all shards are merged to produce the top global `size` results
If k is set, the behaviour instead is following:
- `k` docs is collected from each shard. This `k` docs are used for
combining results with other queries and aggregations on each shard.
- similarly, docs from all shards are merged to produce the top global `size`
results.
Having `k` param makes it more intuitive for users to address their needs.
They also don't need to care and can skip `num_candidates` param for this query
as it is of more internal details to tune how knn search operates.
Closes#108473
* Remove `es-test-dir` book-scoped variable
* Remove `plugins-examples-dir` book-scoped variable
* Remove `:dependencies-dir:` and `:xes-repo-dir:` book-scoped variables
- In `index.asciidoc`, two variables (`:dependencies-dir:` and `:xes-repo-dir:`) were removed.
- In `sql/index.asciidoc`, the `:sql-tests:` path was updated to fuller path
- In `esql/index.asciidoc`, the `:esql-tests:` path was updated idem
* Replace `es-repo-dir` with `es-ref-dir`
* Move `:include-xpack: true` to few files that use it, remove from index.asciidoc
* Add modelId and modelText to KnnVectorQueryBuilder
Use QueryVectorBuilder within KnnVectorQueryBuilder to make it
possible to perform knn queries also when a query vector is not
immediately available. Supplying a text_embedding query_vector_builder
with model_text and model_id instead of the query_vector will result
in the generation of a query_vector by calling inference on the
specified model_id with the supplied model_text (during query
rewrite). This is consistent with the way query vectors are built
from model_id / model_text in KnnSearchBuilder (DFS phase).
This introduced a new knn query:
- knn query is executed during the Query phase similar to all other queries.
- No k parameter, k defaults to size
- num_candidates is a size of queue for candidates to consider while
search a graph on each shard
- For aggregations: "size" results are collected with total = size * shards.
Aggregations will see size * shards results.
- All filters from DSL are applied as post-filters, except: 1) alias filter
is applied as pre-filter or 2) a filter provided as a parameter
inside knn query.
