fix: widen isBackupAndSyncEnabled type to accept null

Author: mathieuartu

packages/profile-sync-controller/src/controllers/user-storage/UserStorageController.ts

@@ -59,7 +59,7 @@ export type UserStorageControllerState = {
   /**
    * Condition used by UI and to determine if we can use some of the User Storage methods.
    */
-  isBackupAndSyncEnabled: boolean;
+  isBackupAndSyncEnabled: boolean | null;
   /**
    * Loading state for the backup and sync update
    */