Replace CMakeSettings.json with CMakePresets.json

https://devblogs.microsoft.com/cppblog/cmake-presets-integration-in-visual-studio-and-visual-studio-code/

> CMakePresets.json will be a recommended alternative to CMakeSettings.json.
> Visual Studio will never read from both CMakePresets.json and CMakeSettings.json at the same time.

It's a good idea to replace our [example/CMakeSettings.json](https://github.com/boostorg/gil/blob/0dc68398b8c01fc0907906be145b6e8dbf77e753/example/cmake/CMakeSettings.json) with the presets file.

Read the linked Microsoft article about CMake presets, then inspect example/cmake/CMakeSettings.json. Replace that example configuration with a CMakePresets.json file and remove the old settings file; done means the example uses the recommended preset format without retaining both files.

Written by the indexing model from the issue text.