Add e-signature support and improve PDF signing process

Introduced `ESignParams` for configurable e-signature settings,
including `ApplicationName` and `DefaultReason`. Updated
`DocReceiverElementDto` and `PdfSignOptionsDto` to support
new properties. Registered `ESignParams` in DI container.

Refactored `SignPdfByElementCommand` to include new fields
and improved error handling. Added `SignPdfByEnvelopeReceiverCommand`
to enable signing documents for envelope receivers.

Replaced DevExpress with PdfSharp for PDF rendering in
`ReceiverSignedPage.razor`, improving layout and flexibility.
Enhanced `PdfSignatureController` with a new endpoint for
signing documents by envelope key.

Added `DataIntegrityException` for better error handling.
Updated `appsettings.json` with `ESignParams` configuration.

EnvelopeGenerator.Application/EnvelopeReceivers/Queries/ReadEnvelopeReceiverSecretQuery.cs

@@ -21,7 +21,24 @@ namespace EnvelopeGenerator.Application.EnvelopeReceivers.Queries;
 /// </remarks>
 public record ReadEnvelopeReceiverSecretQuery
     : EnvelopeReceiverQueryBase<ReadEnvelopeQuery, ReadReceiverQuery>,
-      IRequest<EnvelopeReceiverSecretDto?>;
+      IRequest<EnvelopeReceiverSecretDto?>
+{
+    /// <summary>
+    /// 
+    /// </summary>
+    public ReadEnvelopeReceiverSecretQuery() { }
+
+    /// <summary>
+    /// 
+    /// </summary>
+    /// <param name="envelopeId"></param>
+    /// <param name="receiverId"></param>
+    public ReadEnvelopeReceiverSecretQuery(int envelopeId, int receiverId)
+    {
+        Envelope.Id = envelopeId;
+        Receiver.Id = receiverId;
+    }
+}
 
 /// <summary>
 /// Extension methods for dispatching <see cref="ReadEnvelopeReceiverSecretQuery"/> via <see cref="IMediator"/>.