[Docs] Correct default scroll_size for update by query (#63656)

The current _update_by_query documentation mentions a scroll_size default of 100 and later another default of 1000.
We use the default of 1000 defined in AbstractBulkByScrollRequest and this PR changes the documentation accordingly.

Closes #63637

Author: Christoph Büscher

docs/reference/rest-api/common-parms.asciidoc

@@ -788,7 +788,7 @@ end::scroll[]
 tag::scroll_size[]
 `scroll_size`::
 (Optional, integer) Size of the scroll request that powers the operation.
-Defaults to 100.
+Defaults to 1000.
 end::scroll_size[]
 
 tag::search-failures[]