feat(SaveDocStatusCommand): add IMediator extension methods for saving and signing document status

- Introduced `SaveDocStatusAsync` extension method on IMediator to simplify saving document status
- Added `SignDocAsync` extension method as a shortcut for signing document status
- Refactored `SaveDocStatusCommand` usage to support new mediator extension

EnvelopeGenerator.Application/DocStatus/Commands/SaveDocStatusCommand.cs

@@ -13,6 +13,37 @@ namespace EnvelopeGenerator.Application.DocStatus.Commands;
 /// </summary>
 public record SaveDocStatusCommand : ModifyDocStatusCommandBase, IRequest<int?>;
 
+/// <summary>
+/// 
+/// </summary>
+public static class Extensions
+{
+    /// <summary>
+    /// 
+    /// </summary>
+    /// <param name="mediator"></param>
+    /// <param name="key"></param>
+    /// <param name="value"></param>
+    /// <returns></returns>
+    public static Task<int?> SaveDocStatusAsync(this IMediator mediator, string key, string? value = null)
+    {
+        return mediator.Send(new SaveDocStatusCommand()
+        {
+            Key = key,
+            Value = value
+        });
+    }
+
+    /// <summary>
+    /// 
+    /// </summary>
+    /// <param name="mediator"></param>
+    /// <param name="key"></param>
+    /// <param name="value"></param>
+    /// <returns></returns>
+    public static Task<int?> SignDocAsync(this IMediator mediator, string key, string value) => mediator.SaveDocStatusAsync(value);
+}
+
 /// <summary>
 /// 
 /// </summary>