Add support for generating result PDFs

Introduced the `ResultFilePath` property in the `ZugferdInvoice` model to store the path of generated result PDFs. Added a new service, `PdfResultPackageService`, to create result PDFs by converting the original PDF to PDF/A-3b format and attaching a report file. Updated `Upload.cshtml` and `Upload.cshtml.cs` to handle and display the `ResultFilePath`.

Created a migration to add the `ResultFilePath` column to the database. Updated `Program.cs` to register the new service and added configuration sections in `appsettings.json` for input and output directories. Enhanced error handling and logging for better traceability.

DXApp.TemplateKitProject/Migrations/AppDbContextModelSnapshot.cs

@@ -51,6 +51,9 @@ namespace DXApp.TemplateKitProject.Migrations
                     b.Property<string>("RawXml")
                         .HasColumnType("nvarchar(max)");
 
+                    b.Property<string>("ResultFilePath")
+                        .HasColumnType("nvarchar(max)");
+
                     b.Property<string>("SellerName")
                         .HasColumnType("nvarchar(max)");