Add macOS prerequisite of CLI Tools package

What does this merge request do and why?

If macOS was upgraded, the Command Line Tools package seems to be required for Git to work. Or else this error appears when installing GDK: xcrun: error: invalid active developer path (/Library/Developer/CommandLineTools), missing xcrun at: /Library/Developer/CommandLineTools/usr/bin/xcrun.

Solution from https://apple.stackexchange.com/questions/254380/why-am-i-getting-an-invalid-active-developer-path-when-attempting-to-use-git-a

Impacted categories

The following categories relate to this merge request:

• gdk-reliability - e.g. When a GDK action fails to complete.
• gdk-usability - e.g. Improvements or suggestions around how the GDK functions.
• gdk-performance - e.g. When a GDK action is slow or times out.

Merge request checklist

• This change is backward compatible. If not, please include steps to communicate to our users.
• [-] Tests added for new functionality. If not, please raise an issue to follow-up.
• Documentation added/updated, if needed.
• [-] gdk doctor test added, if needed.
• [-] Add the ~highlight label if this MR should be included in the CHANGELOG.md.