feat: add default template, add sample.

demo/Ursa.Demo/Pages/DrawerDemo.axaml

@@ -13,5 +13,6 @@
     <StackPanel HorizontalAlignment="Left" >
         <u:EnumSelector EnumType="{x:Type common:Position}" Value="{Binding SelectedPosition}"></u:EnumSelector>
         <Button Content="Call Drawer" HorizontalAlignment="Stretch" Command="{Binding OpenDrawerCommand}"></Button>
+        <Button Content="Default Drawer" Command="{Binding OpenDefaultDrawerCommand}"></Button>
     </StackPanel>
 </UserControl>

demo/Ursa.Demo/ViewModels/DrawerDemoViewModel.cs

@@ -13,6 +13,7 @@ namespace Ursa.Demo.ViewModels;
 public partial class DrawerDemoViewModel: ObservableObject
 {
     public ICommand OpenDrawerCommand { get; set; }
+    public ICommand OpenDefaultDrawerCommand { get; set; }
     
     [ObservableProperty] private Position _selectedPosition;
     
@@ -20,6 +21,19 @@ public partial class DrawerDemoViewModel: ObservableObject
     public DrawerDemoViewModel()
     {
         OpenDrawerCommand = new AsyncRelayCommand(OpenDrawer);
+        OpenDefaultDrawerCommand = new AsyncRelayCommand(OpenDefaultDrawer);
+        SelectedPosition = Position.Right;
+    }
+
+    private Task OpenDefaultDrawer()
+    {
+        return Drawer.Show<PlainDialog, PlainDialogViewModel, bool>(new PlainDialogViewModel(), new DefaultDrawerOptions()
+        {
+            Buttons = DialogButton.OKCancel,
+            Position = SelectedPosition,
+            Title = "Please select a date",
+            CanClickOnMaskToClose = false,
+        });
     }
 
     private async Task OpenDrawer()