Add TODO comment

Author: manitgupta

v2/spanner-to-sourcedb/src/main/java/com/google/cloud/teleport/v2/templates/transforms/AssignShardIdFn.java

@@ -187,6 +187,7 @@ public void processElement(ProcessContext c) throws Exception {
         qualifiedShard = this.shardName;
       } else {
         // Skip from processing if table not in session File
+        //TODO: remove dependency on session file when session file is made optional
         boolean doesTableExist = doesTableExistInSessionFile(tableName);
         if (!doesTableExist) {
           LOG.warn(