add maintenance mode & improve & bugfixing

ModpackUpdater.Manager/UpdateCheckOptions.cs

@@ -0,0 +1,10 @@
+using ModpackUpdater.Model;
+
+namespace ModpackUpdater.Manager;
+
+public class UpdateCheckOptions
+{
+    public bool IgnoreMaintenance { get; set; }
+    public bool AllowUpdaterAfterInstall { get; set; } = true;
+    public Side Side { get; set; } = Side.Client;
+}