Updated the `DocumentCreateCommand` record to include a nullable `DataAsBase64` property for better encapsulation. Enhanced the `EnvelopeReceiverController` with logic to validate document data, ensuring that either `DataAsBase64` or `DataAsByte` is provided, but not both. Introduced a new static method `IsBase64String` to validate base64 string format.
- Updated DependencyInjection to include new command handler.
- Modified CreateEnvelopeReceiverCommand for nullable responses.
- Altered SQL command in EnvelopeReceiverAddReadSQL.
- Refactored EnvelopeReceiverController with new dependencies and improved CreateAsync method.
- Expanded appsettings.json with additional configuration settings.
- Introduced new DTOs for signatures and receivers in CreateEnvelopeReceiverDtos.