…27647)

#124581) (#127644)

* New `vector_rescore` parameter as a quantized index type option (#124581)

This adds a new parameter to the quantized index mapping that allows
default oversampling and rescoring to occur.

This doesn't adjust any of the defaults. It allows it to be configured.
When the user provides `rescore_vector: {oversample: <number>}` in the
query it will overwrite it.

For example, here is how to use it with bbq:

```
PUT rescored_bbq
{
  "mappings": {
    "properties": {
      "vector": {
        "type": "dense_vector",
        "index_options": {
          "type": "bbq_hnsw",
          "rescore_vector": {"oversample": 3.0}
        }
      }
    }
  }
}
```

Then, when querying, it will auto oversample the `k` by `3x` and rerank
with the raw vectors.

```
POST _search
{
  "knn": {
    "query_vector": [...],
    "field": "vector"
  }
}
```

(cherry picked from commit b2c1c4e)

* Adds new BWC version for 8.19 backport of (#124581) (#127647)

* [CI] Auto commit changes from spotless

---------

Co-authored-by: elasticsearchmachine <infra-root+elasticsearchmachine@elastic.co>

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