`maintainer-guide.md` not updated to use `VCPKG_LOCK_FIND_PACKAGE_<Pkg>`

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VCPKG_LOCK_FIND_PACKAGE_<Pkg> is documented as a more reliable alternative to CMake's CMAKE_REQUIRE_FIND_PACKAGE_<Pkg> and CMAKE_DISABLE_FIND_PACKAGE_<Pkg> flags, but maintainer-guide.md#when-defining-features-explicitly-control-dependencies does not demonstrate their usage. This can cause new or updated ports following the PR checklist to use outdated script.

The examples could probably be updated to use VCPKG_LOCK_FIND_PACKAGE_<Pkg> as follows:

set(VCPKG_LOCK_FIND_PACKAGE_ZLIB OFF)
if ("zlib" IN_LIST FEATURES)
  set(VCPKG_LOCK_FIND_PACKAGE_ZLIB ON)
endif()

vcpkg_cmake_configure(
  SOURCE_PATH ${SOURCE_PATH}
  OPTIONS
    -DVCPKG_LOCK_FIND_PACKAGE_ZLIB=${VCPKG_LOCK_FIND_PACKAGE_ZLIB}
)

vcpkg_check_features(OUT_FEATURE_OPTIONS FEATURE_OPTIONS
  FEATURES
    "zlib"    VCPKG_LOCK_FIND_PACKAGE_ZLIB
)

vcpkg_cmake_configure(
    SOURCE_PATH ${SOURCE_PATH}
    OPTIONS
      ${FEATURE_OPTIONS}
)

In addition it should probably be mentioned that VCPKG_LOCK_FIND_PACKAGE_<Pkg> is the preferred alternative to CMAKE_REQUIRE_FIND_PACKAGE_<Pkg> and CMAKE_DISABLE_FIND_PACKAGE_<Pkg>.