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/appsettings.json

@@ -11,5 +11,11 @@
   },
   "PdfExtraction": {
     "OutputDirectory": "C:\\PdfExtractions"
+  },
+  "PdfResultReports": {
+    "InputDirectory": "C:\\PdfResultReports"
+  },
+  "PdfResults": {
+    "OutputDirectory": "C:\\PdfResults"
   }
 }