[PM-14484] ApiService showing html in error message (#14658)

* Make ApiService more testable

* Add ApiService tests

* Switch to only reading text/plain content

apps/browser/src/background/main.background.ts

@@ -720,6 +720,7 @@ export default class MainBackground {
       this.logService,
       (logoutReason: LogoutReason, userId?: UserId) => this.logout(logoutReason, userId),
       this.vaultTimeoutSettingsService,
+      { createRequest: (url, request) => new Request(url, request) },
     );
 
     this.fileUploadService = new FileUploadService(this.logService, this.apiService);