added create models for alarms

lib/model/callback_models/create_alarm_request.dart

@@ -0,0 +1,3 @@
+class CreateAlarmRequest {
+  const CreateAlarmRequest();
+}

lib/model/callback_models/create_location_alarm_request.dart

@@ -0,0 +1,13 @@
+import '../location.dart';
+import 'create_alarm_request.dart';
+
+class CreateLocationAlarmRequest extends CreateAlarmRequest {
+  final Location location;
+
+  final int radiusMeters;
+
+  const CreateLocationAlarmRequest({
+    required this.location,
+    required this.radiusMeters,
+  });
+}

lib/model/callback_models/create_time_alarm_request.dart

@@ -0,0 +1,7 @@
+import 'create_alarm_request.dart';
+
+class CreateTimeAlarmRequest extends CreateAlarmRequest {
+  final DateTime triggerAt;
+
+  CreateTimeAlarmRequest({required this.triggerAt});
+}