add availability to oversample value of 0 (elastic#131707)

(cherry picked from commit 4dd124b)

Author: shainaraskas

docs/reference/elasticsearch/mapping-reference/dense-vector.md

@@ -277,7 +277,10 @@ $$$dense-vector-index-options$$$
 :   (Optional, object) An optional section that configures automatic vector rescoring on knn queries for the given field. Only applicable to quantized index types.
 :::::{dropdown} Properties of rescore_vector
 `oversample`
-:   (required, float) The amount to oversample the search results by. This value should be greater than `1.0` and less than `10.0` or exactly `0` to indicate no oversampling & rescoring should occur. The higher the value, the more vectors will be gathered and rescored with the raw values per shard.
+:   (required, float) The amount to oversample the search results by. This value should be one of the following: 
+    * Greater than `1.0` and less than `10.0` 
+    * Exactly `0` to indicate no oversampling and rescoring should occur {applies_to}`stack: ga 9.1`
+    :   The higher the value, the more vectors will be gathered and rescored with the raw values per shard.
     :   In case a knn query specifies a `rescore_vector` parameter, the query `rescore_vector` parameter will be used instead.
     :   See [oversampling and rescoring quantized vectors](docs-content://solutions/search/vector/knn.md#dense-vector-knn-search-rescoring) for details.
 :::::

docs/reference/query-languages/query-dsl/query-dsl-knn-query.md

@@ -113,7 +113,9 @@ Rescoring only makes sense for quantized vectors; when [quantization](/reference
     * Retrieve `num_candidates` candidates per shard.
     * From these candidates, the top `k * oversample` candidates per shard will be rescored using the original vectors.
     * The top `k` rescored candidates will be returned.
-    Must be >= 1f to indicate oversample factor, or exactly `0` to indicate that no oversampling and rescoring should occur.
+    Must be one of the following values: 
+      * \>= 1f to indicate the oversample factor
+      * Exactly `0` to indicate that no oversampling and rescoring should occur. {applies_to}`stack: ga 9.1`
 
 
 See [oversampling and rescoring quantized vectors](docs-content://solutions/search/vector/knn.md#dense-vector-knn-search-rescoring) for details.