feat(*): add additionalAdjustments prop to AppConfig

[ddaribo]

Closes IgniteUI/igniteui-angular-samples#3598

Adds an additionalAdjustments property to the AppConfig interface.
Before the migration to standalone components, additionalAdjustments was part of AppModuleConfig, however, as it is no logner used, the former was left out.
With the propsoed implementation, the additional adjustments will be written to the app.config.ts file.

Example for the dock-manager case and the defineCustomElements invocation:

//...
import { provideAnimations } from '@angular/platform-browser/animations';
import { defineCustomElements } from 'igniteui-dockmanager/loader';
defineCustomElements();


export const AppConfig: ApplicationConfig = {
    providers: [ 
  //...