s3: DeleteBucket to use listing before returning bucket not empty error (#20301)

Use Walk(), which is a recursive listing with versioning, to check if 
the bucket has some objects before being removed. This is beneficial
because the bucket can contain multiple dangling objects in multiple
drives.

Also, this will prevent a bug where a bucket is deleted in a deployment
that has many erasure sets but the bucket contains one or few objects
not spread to enough erasure sets.

cmd/object-api-interface.go

@@ -145,6 +145,7 @@ type WalkOptions struct {
 	LatestOnly   bool                     // returns only latest versions for all matching objects
 	AskDisks     string                   // dictates how many disks are being listed
 	VersionsSort WalkVersionsSortOrder    // sort order for versions of the same object; default: Ascending order in ModTime
+	Limit        int                      // maximum number of items, 0 means no limit
 }
 
 // ExpirationOptions represents object options for object expiration at objectLayer.