Add optimization flags (#16098) (#17476)

Author: denis0x0D

ydb/core/kqp/host/kqp_host.cpp

@@ -1976,6 +1976,9 @@ class TKqpHost : public IKqpHost {
                 || settingName == "TimeOrderRecoverAhead"
                 || settingName == "TimeOrderRecoverRowLimit"
                 || settingName == "MatchRecognizeStream"
+                || settingName == "OptimizerFlags"
+                || settingName == "FuseEquiJoinsInputMultiLabels"
+                || settingName == "PullUpFlatMapOverJoinMultipleLabels"
                 ;
         };
         auto configProvider = CreateConfigProvider(*TypesCtx, gatewaysConfig, {}, allowSettings);

ydb/core/kqp/ut/join/kqp_join_ut.cpp

@@ -616,6 +616,7 @@ Y_UNIT_TEST_SUITE(KqpJoin) {
         {
             auto result = session.ExecuteDataQuery(Q_(R"(
                 PRAGMA FilterPushdownOverJoinOptionalSide;
+                PRAGMA config.flags("OptimizerFlags", "FuseEquiJoinsInputMultiLabels", "PullUpFlatMapOverJoinMultipleLabels");
 
                 SELECT t1.Key1, t1.Key2, t1.Fk1, t1.Value, t2.Key, t2.Value, t3.Key, t3.Value
 
@@ -639,6 +640,7 @@ Y_UNIT_TEST_SUITE(KqpJoin) {
         {
             auto result = session.ExecuteDataQuery(Q_(R"(
                 PRAGMA FilterPushdownOverJoinOptionalSide;
+                PRAGMA config.flags("OptimizerFlags", "FuseEquiJoinsInputMultiLabels", "PullUpFlatMapOverJoinMultipleLabels");
 
                 SELECT t1.Key1, t1.Key2, t1.Fk1, t1.Value, t2.Key, t2.Value, t3.Key, t3.Value