Add log when download completes with file size (#15224) (#15348)

(cherry picked from commit 0ca4ed0)

Signed-off-by: Gaurav Bafna <[email protected]>
Signed-off-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

Author: opensearch-trigger-bot[bot]

server/src/main/java/org/opensearch/index/store/RemoteStoreFileDownloader.java

@@ -149,6 +149,7 @@ private void copyOneFile(
                 try {
                     cancellableThreads.executeIO(() -> {
                         destination.copyFrom(source, file, file, IOContext.DEFAULT);
+                        logger.trace("Downloaded file {} of size {}", file, destination.fileLength(file));
                         onFileCompletion.run();
                         if (secondDestination != null) {
                             secondDestination.copyFrom(destination, file, file, IOContext.DEFAULT);