add set scheduling api

backend/app/Schedule/CreateScheduleAssignmentDto.php

@@ -0,0 +1,15 @@
+<?php
+
+namespace App\Schedule;
+
+use App\Element\Element;
+use DateTimeImmutable;
+
+final readonly class CreateScheduleAssignmentDto
+{
+    public function __construct(
+        public Element $element,
+        public DateTimeImmutable $scheduledDate,
+        public int $position,
+    ) {}
+}