Added api for custom timetable events

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

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+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);
+  }
+}

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

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+import 'package:json_annotation/json_annotation.dart';
+
+import '../customTimetableEvent.dart';
+
+part 'addCustomTimetableEventParams.g.dart';
+
+@JsonSerializable(explicitToJson: true)
+class AddCustomTimetableEventParams {
+  String user;
+  CustomTimetableEvent event;
+
+  AddCustomTimetableEventParams(this.user, this.event);
+
+  factory AddCustomTimetableEventParams.fromJson(Map<String, dynamic> json) => _$AddCustomTimetableEventParamsFromJson(json);
+  Map<String, dynamic> toJson() => _$AddCustomTimetableEventParamsToJson(this);
+}

lib/api/mhsl/customTimetableEvent/add/addCustomTimetableEventParams.g.dart

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+// GENERATED CODE - DO NOT MODIFY BY HAND
+
+part of 'addCustomTimetableEventParams.dart';
+
+// **************************************************************************
+// JsonSerializableGenerator
+// **************************************************************************
+
+AddCustomTimetableEventParams _$AddCustomTimetableEventParamsFromJson(
+        Map<String, dynamic> json) =>
+    AddCustomTimetableEventParams(
+      json['user'] as String,
+      CustomTimetableEvent.fromJson(json['event'] as Map<String, dynamic>),
+    );
+
+Map<String, dynamic> _$AddCustomTimetableEventParamsToJson(
+        AddCustomTimetableEventParams instance) =>
+    <String, dynamic>{
+      'user': instance.user,
+      'event': instance.event.toJson(),
+    };