feat(i18n): add success message for EPG fetch

Adds a new translation key "FETCH_SUCCESS" to English 
localization, providing a success for when 
the EPG is fetched successfully. This improves user 
feedback and enhances the overall user experience.

src/assets/i18n/en.json

@@ -192,7 +192,8 @@
       "DESCRIPTION": "Description",
       "LANGUAGE": "Language",
       "SHOW_PROGRAM_DETAILS": "Show details about this program"
-    }
+    },
+    "FETCH_SUCCESS": "EPG was fetched successfully"
   },
   "LANGUAGES": {
     "ENGLISH": "English",