feat(ads): add interstitial ad trigger when selecting a country

- Import InterstitialAdManager in followed_countries_list_page.dart
- Add onPotentialAdTrigger call in the onTap event of country list items

Author: fulleni

lib/account/view/manage_followed_items/countries/followed_countries_list_page.dart

@@ -2,6 +2,7 @@ import 'package:core/core.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_bloc/flutter_bloc.dart';
 import 'package:flutter_news_app_mobile_client_full_source_code/account/bloc/account_bloc.dart';
+import 'package:flutter_news_app_mobile_client_full_source_code/ads/interstitial_ad_manager.dart';
 import 'package:flutter_news_app_mobile_client_full_source_code/l10n/l10n.dart';
 import 'package:flutter_news_app_mobile_client_full_source_code/router/routes.dart';
 import 'package:go_router/go_router.dart';
@@ -96,6 +97,9 @@ class FollowedCountriesListPage extends StatelessWidget {
                   },
                 ),
                 onTap: () {
+                  context
+                      .read<InterstitialAdManager>()
+                      .onPotentialAdTrigger(context: context);
                   context.pushNamed(
                     Routes.entityDetailsName,
                     pathParameters: {