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/command/mount_std_test.go

@@ -0,0 +1,52 @@
+//go:build linux || darwin || freebsd
+// +build linux darwin freebsd
+
+package command
+
+import "testing"
+
+func Test_bucketPathForMountRoot(t *testing.T) {
+	tests := []struct {
+		name      string
+		mountRoot string
+		expected  string
+		ok        bool
+	}{
+		{
+			name:      "bucket root mount",
+			mountRoot: "/buckets/test",
+			expected:  "/buckets/test",
+			ok:        true,
+		},
+		{
+			name:      "bucket root with trailing slash",
+			mountRoot: "/buckets/test/",
+			expected:  "/buckets/test",
+			ok:        true,
+		},
+		{
+			name:      "subdirectory mount",
+			mountRoot: "/buckets/test/data",
+			expected:  "",
+			ok:        false,
+		},
+		{
+			name:      "non-bucket mount",
+			mountRoot: "/data/test",
+			expected:  "",
+			ok:        false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			gotPath, gotOK := bucketPathForMountRoot(tt.mountRoot, "/buckets")
+			if gotOK != tt.ok {
+				t.Fatalf("expected ok=%v, got %v", tt.ok, gotOK)
+			}
+			if gotPath != tt.expected {
+				t.Fatalf("expected path %q, got %q", tt.expected, gotPath)
+			}
+		})
+	}
+}