TF-1861 Config and abstraction work manager

(cherry picked from commit ee2dca9b34a907c8356ceccf0b23efba2893a01c)

lib/features/offline_mode/config/work_manager_config.dart

@@ -0,0 +1,19 @@
+
+import 'package:core/core.dart';
+import 'package:tmail_ui_user/features/offline_mode/manager/work_dispatcher.dart';
+import 'package:workmanager/workmanager.dart';
+
+class WorkManagerConfig {
+  static WorkManagerConfig? _instance;
+
+  WorkManagerConfig._();
+
+  factory WorkManagerConfig() => _instance ??= WorkManagerConfig._();
+
+  Future<void> initialize() {
+    return Workmanager().initialize(
+      callbackDispatcher,
+      isInDebugMode: BuildUtils.isDebugMode
+    );
+  }
+}

lib/features/offline_mode/config/work_manager_constants.dart

@@ -0,0 +1,4 @@
+
+class WorkManagerConstants {
+  static const String sendingEmailUniqueId = 'com.linagora.ios.teammail.sendingQueue';
+}