Multi Monitor Wallpaper customization

### Description of the new feature / enhancement

I'd like granular wallpaper customization across multi monitors. I just do not want a single wallpaper that can be stretched across all monitors, but a way of grouping certain monitors together and applying custom wallpapers for each group.

### Scenario when this would be used?

I have multiple monitor setup with different resolutions and different groups. Each of these groups require wallpapers that can be stretched across in a customizable way, and make them look nice.

### Supporting information

_No response_

No files, tests, or entry points are mentioned. Start by locating PowerToys' existing multi-monitor wallpaper handling and determine how monitor groups and wallpaper settings are represented; done means groups can receive independently configured wallpapers that accommodate different resolutions.

Written by the indexing model from the issue text.