Better Logging S3 Bulk Delete Failures (#50203)

Unfortunately bulk delete exceptions don't show the individual delete
errors when a bulk delete fails when you log them outright so I added this work-around
to get the individual details to get useful logging.

plugins/repository-s3/src/main/java/org/elasticsearch/repositories/s3/S3BlobContainer.java

@@ -32,6 +32,9 @@ import com.amazonaws.services.s3.model.PartETag;
 import com.amazonaws.services.s3.model.PutObjectRequest;
 import com.amazonaws.services.s3.model.UploadPartRequest;
 import com.amazonaws.services.s3.model.UploadPartResult;
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
+import org.apache.logging.log4j.message.ParameterizedMessage;
 import org.apache.lucene.util.SetOnce;
 import org.elasticsearch.ExceptionsHelper;
 import org.elasticsearch.common.Nullable;
@@ -61,6 +64,8 @@ import static org.elasticsearch.repositories.s3.S3Repository.MIN_PART_SIZE_USING
 
 class S3BlobContainer extends AbstractBlobContainer {
 
+    private static final Logger logger = LogManager.getLogger(S3BlobContainer.class);
+
     /**
      * Maximum number of deletes in a {@link DeleteObjectsRequest}.
      * @see <a href="https://docs.aws.amazon.com/AmazonS3/latest/API/multiobjectdeleteapi.html">S3 Documentation</a>.
@@ -189,6 +194,10 @@ class S3BlobContainer extends AbstractBlobContainer {
                         outstanding.removeAll(keysInRequest);
                         outstanding.addAll(
                             e.getErrors().stream().map(MultiObjectDeleteException.DeleteError::getKey).collect(Collectors.toSet()));
+                        logger.warn(
+                            () -> new ParameterizedMessage("Failed to delete some blobs {}", e.getErrors()
+                                .stream().map(err -> "[" + err.getKey() + "][" + err.getCode() + "][" + err.getMessage() + "]")
+                                .collect(Collectors.toList())), e);
                         aex = ExceptionsHelper.useOrSuppress(aex, e);
                     } catch (AmazonClientException e) {
                         // The AWS client threw any unexpected exception and did not execute the request at all so we do not