Add an experimental label for 2048 vector dims (#95395)

Add an experimental lable for increased vector dims.

Relates to PR#95257

Author: mayya-sharipova

docs/reference/mapping/types/dense-vector.asciidoc

@@ -112,7 +112,11 @@ integer values between -128 to 127, inclusive for both indexing and searching.
 
 `dims`::
 (Required, integer)
-Number of vector dimensions. Can't exceed `2048`.
+Number of vector dimensions. Can't exceed `1024` for indexed vectors
+(`"index": true`), or `2048` for non-indexed vectors.
+
+experimental::[]
+Number of dimensions for indexed vectors can be extended up to `2048`.
 
 `index`::
 (Optional, Boolean)