Add Swiss QR Code extraction feature

Introduced DTOs for request and response to handle Swiss QR Code extraction from PDF documents. Implemented `ExtractSwissQrCodeHandler` to process the extraction using `ISwissQrCodeProcessor`. Added validation for the query with `ExtractSwissQrCodeValidator`. Developed unit tests to ensure correct behavior for successful and failure scenarios.

DocumentOperator.Application/Common/DTOs/ExtractSwissQrCodeRequest.cs

@@ -0,0 +1,12 @@
+namespace DocumentOperator.Application.Common.DTOs;
+
+/// <summary>
+/// Request to extract Swiss QR Code from a PDF document.
+/// The QR code must be located on the last page of the document.
+/// </summary>
+/// <param name="References">Array of reference strings to pass through in the response</param>
+/// <param name="Base64Pdf">PDF document encoded as Base64 string</param>
+public record ExtractSwissQrCodeRequest(
+    IReadOnlyList<string> References,
+    string Base64Pdf
+);