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.Domain/Exceptions/DataIntegrityException.cs

@@ -0,0 +1,13 @@
+#if NETFRAMEWORK
+using System;
+#endif
+
+namespace EnvelopeGenerator.Domain.Exceptions
+{
+    public class DataIntegrityException : Exception
+    {
+        public DataIntegrityException(string message) : base(message)
+        {
+        }
+    }
+}