Added in InstallId so that Kavita owned Email service can validate if requests are valid or not. (#1036)

API/DTOs/Email/ConfirmationEmailDto.cs

@@ -5,4 +5,8 @@ public class ConfirmationEmailDto
     public string InvitingUser { get; init; }
     public string EmailAddress { get; init; }
     public string ServerConfirmationLink { get; init; }
+    /// <summary>
+    /// InstallId of this Kavita Instance
+    /// </summary>
+    public string InstallId { get; init; }
 }