bug: @appium/xcode cannot get xcode CLT version on newer macOS

I'm not sure what "newer" is defined as, but on Big Sur brew config surfaces this info, so they found out how to find out.

Copy whatever brew config does for Big Sur
If brew config does something for other macOS versions which we support...copy that too.
Otherwise, see https://apple.stackexchange.com/questions/180957/determine-xcode-command-line-tools-version

appium / appium-ios