[Backport stable-25-3-1] Use default value of BufferPageAllocSize from proto (#28310)

Author: abyss7

ydb/core/kqp/executer_actor/kqp_executer_impl.h

@@ -156,10 +156,7 @@ class TKqpExecuterBase : public TActor<TDerived> {
         , TasksGraph(Request.TxAlloc, partitionPrunerConfig, AggregationSettings, Counters, BufferActorId)
     {
         ArrayBufferMinFillPercentage = executerConfig.TableServiceConfig.GetArrayBufferMinFillPercentage();
-
-        if (executerConfig.TableServiceConfig.HasBufferPageAllocSize()) {
-            BufferPageAllocSize = executerConfig.TableServiceConfig.GetBufferPageAllocSize();
-        }
+        BufferPageAllocSize = executerConfig.TableServiceConfig.GetBufferPageAllocSize();
 
         EnableReadsMerge = *MergeDatashardReadsControl() == 1;
         TasksGraph.GetMeta().Snapshot = IKqpGateway::TKqpSnapshot(Request.Snapshot.Step, Request.Snapshot.TxId);

ydb/core/kqp/executer_actor/kqp_planner.cpp

@@ -224,6 +224,9 @@ std::unique_ptr<TEvKqpNode::TEvStartKqpTasksRequest> TKqpPlanner::SerializeReque
         if (ArrayBufferMinFillPercentage) {
             serializedTask->SetArrayBufferMinFillPercentage(*ArrayBufferMinFillPercentage);
         }
+        if (BufferPageAllocSize) {
+            serializedTask->SetBufferPageAllocSize(*BufferPageAllocSize);
+        }
         request.AddTasks()->Swap(serializedTask);
     }