Added api for custom timetable events

lib/api/mhsl/customTimetableEvent/add/addCustomTimetableEvent.dart

@@ -0,0 +1,24 @@
+import 'dart:convert';
+import 'dart:developer';
+
+import 'package:http/http.dart';
+import 'package:http/http.dart' as http;
+
+import '../../mhslApi.dart';
+import 'addCustomTimetableEventParams.dart';
+
+class AddCustomTimetableEvent extends MhslApi<void> {
+  AddCustomTimetableEventParams params;
+  
+  AddCustomTimetableEvent(this.params) : super('server/timetable/customEvents');
+
+  @override
+  void assemble(String raw) {}
+
+  @override
+  Future<Response>? request(Uri uri) {
+    String body = jsonEncode(params.toJson());
+    log(body);
+    return http.post(uri, body: body);
+  }
+}