Add SignatureDto and mapping for signature handling

Added a new `SignatureDto` record to represent captured signatures with metadata, including properties like `ElementId`, `DataUrl`, `FullName`, `Position`, and `Place`. Updated `SigningCommand` to include a `Signatures` property for handling multiple signatures, deprecating `PsPdfKitAnnotation`.

Introduced a `MappingProfile` class to map `SignatureDto` to `DocReceiverElement` using AutoMapper. Added necessary `using` directives to support the new mapping configuration.

EnvelopeGenerator.Application/DocReceiverElements/MappingProfile.cs

@@ -0,0 +1,19 @@
+using AutoMapper;
+using EnvelopeGenerator.Application.DocReceiverElements.Commands;
+using EnvelopeGenerator.Domain.Entities;
+
+namespace EnvelopeGenerator.Application.DocReceiverElements;
+
+/// <summary>
+///
+/// </summary>
+public class MappingProfile : Profile
+{
+    /// <summary>
+    ///
+    /// </summary>
+    public MappingProfile()
+    {
+        CreateMap<SignatureDto, DocReceiverElement>();
+    }
+}