Replace SignatureDto with new Signature record

Replaced the `SignatureDto` record with a new `Signature` record to provide a more robust representation of signature data. Updated `MappingProfile` to map `Signature` to `DocReceiverElement` and removed the old `SignatureDto` mapping. Updated `SigningCommand` to use `IEnumerable<Signature>` instead of `IEnumerable<SignatureDto>`. Removed the old `MappingProfile` class and adjusted namespaces and `using` directives accordingly. These changes improve maintainability and streamline signature handling.

EnvelopeGenerator.Application/Common/Dto/MappingProfile.cs

@@ -40,6 +40,7 @@ public class MappingProfile : Profile
         // DTO to Entity mappings
         CreateMap<ConfigDto, Config>();
         CreateMap<DocReceiverElementDto, DocReceiverElement>();
+        CreateMap<Signature, DocReceiverElement>().MapChangedWhen();
         CreateMap<DocumentStatusDto, DocumentStatus>();
         CreateMap<EmailTemplateDto, EmailTemplate>();
         CreateMap<EnvelopeDto, Envelope>();