MAUI - Add documentation for SetBeforeScreenshotCapture option

Author: bricefriha

platform-includes/enriching-events/attach-screenshots/dotnet.maui.mdx

@@ -5,5 +5,15 @@ var builder = MauiApp.CreateBuilder()
     {
         options.Dsn = "___PUBLIC_DSN___";
         options.AttachScreenshot = true;
+        
+        // Set a Before Screenshot capture callback to execute some code before the screenshot is taken
+        options.SetBeforeScreenshotCapture((@event, hint) =>
+        {
+              //
+              // Your code here
+              
+              // Return true to capture or false to prevent the capture
+              return true;
+        });
     })
 ```