Added static setting for checkPendingFlushUpdate functionality of luc…

…ene writer

Signed-off-by: Prabhat Sharma <[email protected]>

_install-and-configure/configuring-opensearch/index-settings.md

@@ -100,6 +100,7 @@ OpenSearch supports the following static index-level index settings:
 
 - `index.merge_on_flush.policy` (default | merge-on-flush): This setting controls which merge policy should be used when `index.merge_on_flush.enabled` is enabled. Default is `default`.
 
+- `index.check_pending_flush.enabled` (Boolean): This setting controls Apache Lucene's Index writer setting checkPendingFlushOnUpdate which controls if an indexing thread should check for pending flushes on update in order to help out flushing indexing buffers to disk
 
 ### Updating a static index setting