feat(l10n): add loading headline for filters page in headlines feed

- Add new localization strings for both Arabic and English
- Introduce "headlinesFeedFilterLoadingHeadline" for loading state on headlines filter page
- Update corresponding description for both language files

Author: fulleni

lib/l10n/app_localizations.dart

@@ -1687,6 +1687,12 @@ abstract class AppLocalizations {
   /// In en, this message translates to:
   /// **'Retry'**
   String get retryButtonText;
+
+  /// Headline for the loading state when fetching filter options on the headlines filter page.
+  ///
+  /// In en, this message translates to:
+  /// **'Loading Filters'**
+  String get headlinesFeedFilterLoadingHeadline;
 }
 
 class _AppLocalizationsDelegate

lib/l10n/app_localizations_ar.dart

@@ -880,4 +880,7 @@ class AppLocalizationsAr extends AppLocalizations {
 
   @override
   String get retryButtonText => 'إعادة المحاولة';
+
+  @override
+  String get headlinesFeedFilterLoadingHeadline => 'جاري تحميل الفلاتر';
 }

lib/l10n/app_localizations_en.dart

@@ -882,4 +882,7 @@ class AppLocalizationsEn extends AppLocalizations {
 
   @override
   String get retryButtonText => 'Retry';
+
+  @override
+  String get headlinesFeedFilterLoadingHeadline => 'Loading Filters';
 }

lib/l10n/arb/app_ar.arb

@@ -1148,5 +1148,9 @@
     "retryButtonText": "إعادة المحاولة",
     "@retryButtonText": {
         "description": "Text for a button that allows the user to retry a failed operation."
+    },
+    "headlinesFeedFilterLoadingHeadline": "جاري تحميل الفلاتر",
+    "@headlinesFeedFilterLoadingHeadline": {
+        "description": "Headline for the loading state when fetching filter options on the headlines filter page."
     }
 }

lib/l10n/arb/app_en.arb

@@ -1148,5 +1148,9 @@
     "retryButtonText": "Retry",
     "@retryButtonText": {
         "description": "Text for a button that allows the user to retry a failed operation."
+    },
+    "headlinesFeedFilterLoadingHeadline": "Loading Filters",
+    "@headlinesFeedFilterLoadingHeadline": {
+        "description": "Headline for the loading state when fetching filter options on the headlines filter page."
     }
 }