correct OBJECT ENCODING response for stream type (redis#7797)

This commit makes stream object returning "stream" as encoding type in OBJECT ENCODING subcommand and DEBUG OBJECT command.

Till now, it would return "unknown"

src/object.c

@@ -740,6 +740,7 @@ char *strEncoding(int encoding) {
     case OBJ_ENCODING_INTSET: return "intset";
     case OBJ_ENCODING_SKIPLIST: return "skiplist";
     case OBJ_ENCODING_EMBSTR: return "embstr";
+    case OBJ_ENCODING_STREAM: return "stream";
     default: return "unknown";
     }
 }