[PM-6769] [SM-1158] Fix Translation pipe issues on main (#8319)

* Require init in i18n service.

this is needed to load translations and set translation locale

* No longer need to cast i18n

* Expose user preferred locale in i18nService

This is for correctly displaying `default` when no locale has been set in preferences components. The `locale$` observable should always resolve to the currently locale currently being translated to.

libs/common/src/platform/abstractions/i18n.service.ts

@@ -3,6 +3,8 @@ import { Observable } from "rxjs";
 import { TranslationService } from "./translation.service";
 
 export abstract class I18nService extends TranslationService {
+  userSetLocale$: Observable<string | undefined>;
   locale$: Observable<string>;
   abstract setLocale(locale: string): Promise<void>;
+  abstract init(): Promise<void>;
 }