[PM-2282] Make feature flags type safe (#8612)

Refactors the feature flags in ConfigService to be type safe. It also moves the default value to a centralized location rather than the caller defining it. This ensures consistency across the various places they are used.

libs/angular/src/vault/components/add-edit.component.ts

@@ -182,7 +182,6 @@ export class AddEditComponent implements OnInit, OnDestroy {
   async ngOnInit() {
     this.flexibleCollectionsV1Enabled = await this.configService.getFeatureFlag(
       FeatureFlag.FlexibleCollectionsV1,
-      false,
     );
 
     this.policyService