[Examples] Make sure that clangd-contexts build script has sufficient permissions

[sgraband]

Feature Description:

I just noticed that on my local machine in the electron variant (packaged or built from sources) the generated build.sh script from the clangd-contexts example failed with a permission denied for me. It was an easy fix using chmod +x ./build.sh, but we should either document this or even better, make sure that the file has the correct permissions after we copied it.