LayerDeleter does not return information on deleted objects

Description of Request

I have been coming across some difficulties when deleting S3 layers. Having some information on the result of the delete request would be very interesting for implementing additional logic when failures occur.

Proposed Solution

I would like to see the status or even the unsuccessfully deleted objects of the s3Client.deleteObjects request. Something like in the AWS's documentation.

DeleteObjectsResult delObjRes = s3Client.deleteObjects(multiObjectDeleteRequest);
int successfulDeletes = delObjRes.getDeletedObjects().size();

@pomadchin mentionned that all the backends have their corresponding LayerDeleters fand the error encoding should be encoded with all of them.

Describe alternatives you've considered

I am not sure of the direction the effort should take to synchronize all of the backends. I would be happy to contribute to updating the S3 backend.

The issue mentions LayerDeleter implementations across backends and the S3 client's deleteObjects request, but names no files or tests. First map the LayerDeleter implementations and inspect the S3 deletion call, then define a consistent result or error contract across backends. Done means deletion outcomes are exposed consistently and covered by relevant tests.