add a debug capability to list all metadata keys

weed/filer/filerstore.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"errors"
 	"github.com/chrislusf/seaweedfs/weed/util"
+	"io"
 )
 
 var (
@@ -45,3 +46,7 @@ type BucketAware interface {
 	OnBucketDeletion(bucket string)
 	CanDropWholeBucket() bool
 }
+
+type Debuggable interface {
+	Debug(writer io.Writer)
+}