Deprecate services in favor of MediatR integration

This commit introduces the `[Obsolete("Use MediatR")]` attribute to various service fields and methods across multiple controllers and extension classes, signaling a transition to MediatR for handling requests and commands.

Key changes include:
- Marking `IEnvelopeService`, `IEnvelopeReceiverService`, and `IEnvelopeTypeService` as obsolete in their respective controllers.
- Updating `AddEnvelopeGeneratorInfrastructureServices` to utilize `IRepository`.
- Refactoring `AddCommandManagerRunner` and `CreateHost` methods to indicate obsolescence.
- Replacing `DigitalData.Core.DTO` with `DigitalData.Core.Abstraction.Application.DTO` in using directives.

These changes modernize the codebase and improve command and query handling while cleaning up service dependencies.

EnvelopeGenerator.Infrastructure/DependencyExtensions.cs

@@ -32,6 +32,7 @@ public static class DIExtensions
     /// This method ensures that the repositories are registered as scoped services, meaning that a new instance of each repository 
     /// will be created per HTTP request (or per scope) within the dependency injection container.
     /// </remarks>
+    [Obsolete("Use IRepository")]
     public static IServiceCollection AddEnvelopeGeneratorInfrastructureServices(this IServiceCollection services,
         Action<IServiceProvider, DbContextOptionsBuilder>? dbContextOptions = null,
         IConfiguration? sqlExecutorConfiguration = null,
@@ -157,4 +158,4 @@ public static class DIExtensions
 
         return services;
     }
-}
+}