feat(Background): Add Width, Height, Top and Left properties.

- Add JsonIgnroe property to BackGround

EnvelopeGenerator.Web/Models/Annotation/Background.cs

@@ -1,6 +1,17 @@
-namespace EnvelopeGenerator.Web.Models.Annotation;
+using System.Text.Json.Serialization;
+
+namespace EnvelopeGenerator.Web.Models.Annotation;
 
 public class Background
 {
+    [JsonIgnore]
     public int Margin { get; init; }
+
+    public double? Width { get; set; }
+
+    public double? Height { get; set; }
+
+    public double? Left { get; set; }
+
+    public double? Top { get; set; }
 }