Switch empty-folder cleanup to bucket policy (#8292)

* Fix Spark _temporary cleanup and add issue #8285 regression test

* Generalize empty folder cleanup for Spark temp artifacts

* Revert synchronous folder pruning and add cleanup diagnostics

* Add actionable empty-folder cleanup diagnostics

* Fix Spark temp marker cleanup in async folder cleaner

* Fix Spark temp cleanup with implicit directory markers

* Keep explicit directory markers non-implicit

* logging

* more logs

* Switch empty-folder cleanup to bucket policy

* Seaweed-X-Amz-Allow-Empty-Folders

* less logs

* go vet

* less logs

* refactoring

weed/s3api/s3api_object_handlers_put.go

@@ -139,6 +139,8 @@ func (s3a *S3ApiServer) PutObjectHandler(w http.ResponseWriter, r *http.Request)
 			fullDirPath = fullDirPath + "/" + dirName
 		}
 
+		glog.Infof("PutObjectHandler: explicit directory marker %s/%s (contentType=%q, len=%d)",
+			bucket, object, objectContentType, r.ContentLength)
 		if err := s3a.mkdir(
 			fullDirPath, entryName,
 			func(entry *filer_pb.Entry) {