[docs] Document deprecated functions from #20142 in the maintainer guide.

[BillyONeal]

See discussion at #20142 (comment)

[github-actions]

You have modified or added at least one portfile where deprecated functions are used.

If you feel able to do so, please consider migrating them to the new functions:
vcpkg_install_cmake -> vcpkg_cmake_install (from port vcpkg-cmake)
vcpkg_build_cmake -> vcpkg_cmake_build (from port vcpkg-cmake)
vcpkg_configure_cmake -> vcpkg_cmake_configure (Please remove the option PREFER_NINJA) (from port vcpkg-cmake)
vcpkg_fixup_cmake_targets -> vcpkg_cmake_config_fixup (from port vcpkg-cmake-config)

In the ports that use the new function, you have to add the corresponding dependencies:

{
  "name": "vcpkg-cmake",
  "host": true
},
{
  "name": "vcpkg-cmake-config",
  "host": true
}

The following files are affected:

• ports/openimageio/portfile.cmake

[Osyotr]

Would you kindly also update vcpkg-tool? It suggests to use deprecated vcpkg_fixup_cmake_targets
https://github.com/microsoft/vcpkg-tool/blob/733e90d1bc3f4f8188d57d73e2d20765c232cc26/src/vcpkg/postbuildlint.cpp#L265

[BillyONeal]

Would you kindly also update vcpkg-tool? It suggests to use deprecated vcpkg_fixup_cmake_targets
https://github.com/microsoft/vcpkg-tool/blob/733e90d1bc3f4f8188d57d73e2d20765c232cc26/src/vcpkg/postbuildlint.cpp#L265

Done: microsoft/vcpkg-tool#198