TF-1289: [Data] Implement GetSubscription in fcm repository

lib/features/push_notification/data/local/fcm_cache_manager.dart

@@ -49,4 +49,13 @@ class FCMCacheManager {
     return _fcmSubscriptionCacheClient.insertItem(
         FCMSubscriptionCache.keyCacheValue, fcmSubscriptionCache);
   }
+  
+  Future<FCMSubscriptionCache> getSubscription() async {
+    final _fcmSubscription = await _fcmSubscriptionCacheClient.getItem(FCMSubscriptionCache.keyCacheValue);
+    if (_fcmSubscription == null) {
+      throw NotFoundSubscriptionException();
+    } else {
+      return _fcmSubscription;
+    }
+  }
 }

lib/features/push_notification/data/repository/fcm_repository_impl.dart

@@ -86,6 +86,12 @@ class FCMRepositoryImpl extends FCMRepository {
     return _fcmDatasource[DataSourceType.network]!.registerNewToken(newTokenRequest);
   }
 
+  @override
+  Future<FCMSubscription> getSubscription() async {
+    final _fcmSubScription = await _fcmDatasource[DataSourceType.local]!.geSubscription();
+    return FCMSubscription(_fcmSubScription.deviceId, _fcmSubScription.subscriptionId);
+  }
+  
   @override
   Future<void> storeSubscription(FCMSubscription fcmSubscription) {
     return _fcmDatasource[DataSourceType.local]!.storeSubscription(fcmSubscription.toFCMSubscriptionCache());