dotnet run file support settings.json when using WebApplication.CreateSilmBuilder

### Is your feature request related to a problem? Please describe.

@DamianEdwards currently, we already support load settings.json config when using `WebApplication.Create`/`WebApplication.CreateBuilder`, while for AOT we may want to prefer to use the `WebApplication.CreateSlimBuilder`, when I use it the settings.json configuration does not load as expected as `WebApplication.CreateBuilder` does, since the file-based app enabled PublishAot by default, maybe better to support the settings.json for `WebApplication.CreateSlimBuilder` also?

### Describe the solution you'd like

Load the settings.json for `WebApplication.CreateSlimBuilder` also likes the appsettings.json