feat(DocSignedNotification): replace Annotations with PsPdfKitAnnotation in DocSignedNotification

- Introduced new record `PsPdfKitAnnotation` to encapsulate both Instant and Structured annotation data
- Updated `DocSignedNotification` to use `PsPdfKitAnnotation` instead of `ExpandoObject Annotations`
- Modified extension methods to accept and map `PsPdfKitAnnotation`
- Added reference to `EnvelopeGenerator.Application.Annotations.Commands` for `CreateAnnotationCommand`

EnvelopeGenerator.Application/Common/Notifications/DocSigned/Handlers/HistoryHandler.cs

@@ -2,7 +2,6 @@
 using EnvelopeGenerator.Application.Histories.Commands;
 using EnvelopeGenerator.Domain.Constants;
 using MediatR;
-using Newtonsoft.Json;
 
 namespace EnvelopeGenerator.Application.Common.Notifications.DocSigned.Handlers;