support finding libzlib through pkg-config

[nektro]

the config is setup already for libsodium but not zlib

CMake Error at /home/meghan/cache/-kitware_cmake.bin-3.24.0/share/cmake-3.24/Modules/FindPackageHandleStandardArgs.cmake:230 (message):
  Could NOT find ZLIB (missing: ZLIB_LIBRARY ZLIB_INCLUDE_DIR)
Call Stack (most recent call first):
  /home/meghan/cache/-kitware_cmake.bin-3.24.0/share/cmake-3.24/Modules/FindPackageHandleStandardArgs.cmake:594 (_FPHSA_FAILURE_MESSAGE)
  /home/meghan/cache/-kitware_cmake.bin-3.24.0/share/cmake-3.24/Modules/FindZLIB.cmake:150 (FIND_PACKAGE_HANDLE_STANDARD_ARGS)
  CMakeLists.txt:89 (find_package)