Move NYT::Initialize to separate "weak" hook

Move BEFORE_INIT hook to the beginning
commit_hash:9cbf1d95bf1cda4bcce0d3ab9207debcab65391b

Author: maslinnik

library/cpp/testing/hook/yt_initialize_hook.h

@@ -0,0 +1,6 @@
+#pragma once
+
+// Since we need to call NYT::Initialize immediately on starting the program, we separate it from other BEFORE_INIT hooks.
+// This weak function is overriden in C++ client (see yt/cpp/mapreduce/tests/yt_initialize_hook/yt_hook.cpp).
+__attribute__((weak)) void InitializeYt(int, char**) {
+}

library/cpp/testing/unittest/utmain.cpp

@@ -9,6 +9,7 @@
 #include <library/cpp/json/writer/json_value.h>
 #include <library/cpp/testing/common/env.h>
 #include <library/cpp/testing/hook/hook.h>
+#include <library/cpp/testing/hook/yt_initialize_hook.h>
 
 #include <util/datetime/base.h>
 
@@ -709,6 +710,8 @@ int NUnitTest::RunMain(int argc, char** argv) {
         Y_ABORT_UNLESS(!sigaction(SIGUSR2, &sa, nullptr));
     }
 #endif
+    InitializeYt(argc, argv);
+
     NTesting::THook::CallBeforeInit();
     InitNetworkSubSystem();
     Singleton<::NPrivate::TTestEnv>();