Updated all references to `SignCommand` to use the new `SigningCommand` name for consistency and clarity. This includes changes to class definitions, method signatures, and pipeline behaviors in the following files:
- `DependencyInjection.cs`: Updated pipeline behaviors to use `SigningCommand`.
- `AnnotationBehavior.cs`: Updated class definition and methods to use `SigningCommand`. Marked `SignCommand` as `[Obsolete]`.
- `DocStatusBehavior.cs`, `EnvelopeReceiverResolutionBehavior.cs`, `HistoryBehavior.cs`, `SendSignedMailBehavior.cs`: Updated class definitions and methods to use `SigningCommand`.
- `SendSignedMailBehavior.cs`: Updated `CreatePlaceHolders` method to accept `SigningCommand`.
- `SigningCommand.cs`: Renamed `SignCommand` record to `SigningCommand` and updated internal methods and properties. Renamed `SignCommandHandler` to `SigningCommandHandler`.
Marked `SignCommand` as `[Obsolete]` where applicable to indicate deprecation. These changes improve code readability and align the command name with its purpose in the signing process.
Introduced a new pipeline behavior class `EnvelopeReceiverResolutionBehavior` to resolve and validate the `EnvelopeReceiver` during the signing process.
- Added necessary `using` directives for dependencies such as `AutoMapper`, `MediatR`, and `IRepository`.
- Implemented the `Handle` method to query the database for `EnvelopeReceiver` if not provided in the `SignCommand` request.
- Throws a `NotFoundException` if the `EnvelopeReceiver` is not found.
- Maps the retrieved entity to a DTO and sets it in the request.
- Ensures the behavior executes before other signing process behaviors.
