metacache: Allow prefix filtering (#10920)

Do listings with prefix filter when bloom filter is dirty.

This will forward the prefix filter to the lister which will make it 
only scan the folders/objects with the specified prefix.

If we have a clean bloom filter we try to build a more generally 
useful cache so in that case, we will list all objects/folders.

cmd/metacache-server-sets.go

@@ -100,6 +100,8 @@ func (z *erasureServerSets) listPath(ctx context.Context, o listPathOptions) (en
 			rpc = nil
 			o.Transient = true
 		}
+		// Apply prefix filter if enabled.
+		o.SetFilter()
 		if rpc == nil || o.Transient {
 			// Local
 			cache = localMetacacheMgr.findCache(ctx, o)