Add entry for "Other" applications

### Problem

Apps that aren't in flatpak but use portals will write to the same entry in PermissionStore, but there's no way to change those settings after you see the portal prompt. For example if you try to set a wallpaper from Files, it the portal will ask if it's okay for apps to set the wallpaper, and if you select "No", you'll never get the option again

### Proposal

Include an "Other" item at the end of the apps list like we currently do in notifications so that these settings can be changed later

### Prior Art (Optional)

_No response_