Standard way to include zlib iface header

This allows to use user provided zib when building projects exported
from arcadia to opensource.

DEVTOOLS-9036

ref:7a7994ab05782e4bfb160eb4d3102c4b98efc35c

library/cpp/blockcodecs/codecs/zlib/zlib.cpp

@@ -2,7 +2,7 @@
 #include <library/cpp/blockcodecs/core/common.h>
 #include <library/cpp/blockcodecs/core/register.h>
 
-#include <contrib/libs/zlib/zlib.h>
+#include <zlib.h>
 
 using namespace NBlockCodecs;
 

library/cpp/monlib/encode/spack/compression.cpp

@@ -11,7 +11,7 @@
 
 #include <contrib/libs/lz4/lz4.h>
 #include <contrib/libs/xxhash/xxhash.h>
-#include <contrib/libs/zlib/zlib.h>
+#include <zlib.h>
 #define ZSTD_STATIC_LINKING_ONLY
 #include <contrib/libs/zstd/include/zstd.h>