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

test/s3/spark/issue_8234_repro_test.go

@@ -14,7 +14,7 @@ func setupSparkIssue8234Env(t *testing.T) *TestEnvironment {
 	}
 
 	env.StartSeaweedFS(t)
-	t.Cleanup(func() { env.Cleanup() })
+	t.Cleanup(func() { env.Cleanup(t) })
 
 	createObjectBucket(t, env, "test")
 	env.startSparkContainer(t)