Added `[Obsolete]` attributes to classes, methods, and properties related to the deprecated PSPDFKit library and notifications.
- Marked `AnnotationHandler`, `DocStatusHandler`, `AnnotationBehavior`, and `DocStatusBehavior` as obsolete.
- Marked `Handle` methods in `DocStatusHandler` and `DocStatusBehavior` as obsolete.
- Marked `PsPdfKitAnnotation` property in `SignCommand` as obsolete.
- Marked `CreateOrUpdate` method in `AnnotationController` as obsolete.
- Added `Handle` methods in `DocStatusHandler` and `DocStatusBehavior` to send `CreateDocStatusCommand`.
- Updated `AnnotationController` dependencies to include `EnvelopeGenerator.Application.Common.Dto`.
These changes indicate a transition to `Signature.Commands.SignCommand` and deprecate PSPDFKit-related functionality.
Introduce `SignCommand` and `SignCommandHandler` in the `EnvelopeGenerator.Application.Signature.Commands` namespace.
- `SignCommand` is a CQRS command that encapsulates the envelope receiver's information (`EnvelopeReceiverDto`) and optional PSPDFKit annotation data.
- Added computed properties for email template type (`TemplateType`) and receiver's email address (`EmailAddress`), with validation for null receivers.
- `SignCommandHandler` implements the `IRequestHandler<SignCommand>` interface, with a placeholder `Handle` method delegating processing to pipeline behaviors.
- Added necessary `using` directives for MediatR, DTOs, extensions, and constants.
