[BugFix] Fix grascale upgrade between main and lower version (StarRoc…

…ks#30436)

Introduced by StarRocks#26246.

TOlapScanNode.columns_desc should be optional instead of required.

BTW, some codes in BE use thrift_olap_scan_node.columns_desc directly. This is safe, because the default value of thrift_olap_scan_node.columns_desc is an empty std::vector<>.

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Signed-off-by: zihe.liu <ziheliu1024@gmail.com>

fe/fe-core/src/main/java/com/starrocks/planner/OlapScanNode.java

@@ -838,8 +838,8 @@ protected void toThrift(TPlanNode msg) {
         } else { // If you find yourself changing this code block, see also the above code block
             msg.node_type = TPlanNodeType.OLAP_SCAN_NODE;
             msg.olap_scan_node =
-                    new TOlapScanNode(desc.getId().asInt(), keyColumnNames,
-                        keyColumnTypes, isPreAggregation, columnsDesc);
+                    new TOlapScanNode(desc.getId().asInt(), keyColumnNames, keyColumnTypes, isPreAggregation);
+            msg.olap_scan_node.setColumns_desc(columnsDesc);
             msg.olap_scan_node.setSort_key_column_names(keyColumnNames);
             msg.olap_scan_node.setRollup_name(olapTable.getIndexNameById(selectedIndexId));
             if (!conjuncts.isEmpty()) {

gensrc/thrift/PlanNodes.thrift

@@ -495,7 +495,7 @@ struct TOlapScanNode {
   29: optional list<TColumnAccessPath> column_access_paths
 
   30: optional bool use_pk_index
-  31: required list<Descriptors.TColumn> columns_desc
+  31: optional list<Descriptors.TColumn> columns_desc
   32: optional bool output_chunk_by_bucket
 }