set default ttl back to 36000000 (#4927)

server/src/assembly/resources/conf/iotdb-engine.properties

@@ -191,7 +191,7 @@ timestamp_precision=ms
 # also be affected. And negative values are accepted, which means you can only insert future
 # data.
 # Datatype: long
-# default_ttl=0
+# default_ttl=36000000
 
 # The size of the log buffer in each log node (in bytes). Due to the double buffer mechanism,
 # if WAL is enabled and the size of the inserted plan is greater than one-half of this parameter,