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/storage-rest-common.go

@@ -70,6 +70,7 @@ const (
 	storageRESTLength        = "length"
 	storageRESTCount         = "count"
 	storageRESTMarkerPath    = "marker"
+	storageRESTPrefixFilter  = "prefix"
 	storageRESTRecursive     = "recursive"
 	storageRESTBitrotAlgo    = "bitrot-algo"
 	storageRESTBitrotHash    = "bitrot-hash"