[google-cloud-cpp] Fix features dialogflow-* CMake export

[LilyWangLL]

Describe the pull request

• What does your PR fix?

  Fixes [google-cloud-cpp] Problem compiling dialogflow-es package #26442
  Sorry, I missed the following bug, PR [google-cloud-cpp] Fix wrong parameter "${FEATURES}" #26459 does not fully fix the bugs of these two features. This PR will fix features dialogflow-cx and dialogflow-es CMake export.

Another thing I noticed is that, after the previous change is done and once the process finished compiling, some files and folders were missing in the "packages" folder

In the file "install-x64-windows-rel-out.log" I see (among other lines)

-- Installing: C:/files/repos/other-external/vcpkg/packages/google-cloud-cpp_x64-windows/lib/pkgconfig/google_cloud_cpp_dialogflow_es.pc
-- Installing: C:/files/repos/other-external/vcpkg/packages/google-cloud-cpp_x64-windows/lib/cmake/google_cloud_cpp_dialogflow_es/google_cloud_cpp_dialogflow_es-config.cmake
-- Installing: C:/files/repos/other-external/vcpkg/packages/google-cloud-cpp_x64-windows/lib/cmake/google_cloud_cpp_dialogflow_es/google_cloud_cpp_dialogflow_es-config-version.cmake
-- Installing: C:/files/repos/other-external/vcpkg/packages/google-cloud-cpp_x64-windows/lib/pkgconfig/google_cloud_cpp_dialogflow_es_protos.pc

[JavierMatosD]

Thank you @LilyWangLL :)