PgSyntax feature flag is true by default (#10684)

Author: uzhastik

ydb/core/protos/feature_flags.proto

@@ -150,7 +150,7 @@ message TFeatureFlags {
     optional bool EnableOptionalColumnsInColumnShard = 136 [default = false];
     //optional bool EnableGranularTimecast = 137 [default = true]; NB. exists in main
     optional bool EnableAlterShardingInColumnShard = 138 [default = false];
-    optional bool EnablePgSyntax = 139 [default = false];
+    optional bool EnablePgSyntax = 139 [default = true];
     optional bool EnableTieringInColumnShard = 140 [default = false];
     optional bool EnableMetadataObjectsOnServerless = 141 [default = true];
     optional bool EnableOlapCompression = 142 [default = false];