install_platform: Returns the platform key used to index install_config
Description
Unlike install_os this distinguishes Intel from Apple Silicon
macOS, which are separate entries in install_config because 'PyTorch'
ships different archives for them (and, from 2.2 onwards, none at all for Intel).
Usage
install_platform()
Arguments
Value
one of "linux", "windows", "darwin" or "darwin-arm64"