feat: add envelope delete command and API endpoint

EnvelopeGenerator.Application/Common/Notifications/EnvelopeDeleted/EnvelopeDeletedNotification.cs

@@ -0,0 +1,21 @@
+using EnvelopeGenerator.Domain.Constants;
+using EnvelopeGenerator.Domain.Entities;
+using MediatR;
+
+namespace EnvelopeGenerator.Application.Common.Notifications.EnvelopeDeleted;
+
+public record EnvelopeDeletedNotification : INotification, ISendMailNotification
+{
+    public required Envelope Envelope { get; init; }
+
+    public required EnvelopeReceiver EnvelopeReceiver { get; init; }
+
+    public required string Reason { get; init; }
+
+    public required string SenderReference { get; init; }
+
+    public EmailTemplateType TemplateType => EmailTemplateType.DocumentDeleted;
+
+    public string EmailAddress => EnvelopeReceiver.Receiver?.EmailAddress
+        ?? throw new InvalidOperationException("Receiver email is missing for EnvelopeDeletedNotification.");
+}