api: add events to control api requests via context

Pilz.Net/Api/ApiRequestCancelEventArgs.cs

@@ -0,0 +1,10 @@
+using System.ComponentModel;
+
+namespace Pilz.Net.Api;
+
+public delegate void ApiRequestCancelEventHandler(object sender, ApiRequestCancelEventArgs e);
+
+public class ApiRequestCancelEventArgs(ApiRequestContext context) : CancelEventArgs
+{
+    public ApiRequestContext Context => context;
+}