Add MediatR, FluentValidation, AutoMapper, and EF Core

Updated application and infrastructure layers to include MediatR, FluentValidation, AutoMapper, and Entity Framework Core.

- Added new dependencies to `DigitalData.TaskFlow.Application.csproj` and `DigitalData.TaskFlow.Infrastructure.csproj` for MediatR, FluentValidation, AutoMapper, and EF Core.
- Configured MediatR with options and license key support.
- Registered validators and AutoMapper profiles in the application layer.
- Introduced `MediatROptions` and `SwaggerOptions` for configuration.
- Updated `appsettings.json` with connection strings and configuration sections for MediatR and Swagger.
- Replaced placeholder comments in `DependencyInjection` classes with actual service registrations.
- Upgraded `Swashbuckle.AspNetCore` and added `FluentValidation.AspNetCore` for API validation.

src/infrastructure/DigitalData.TaskFlow.Infrastructure/DependencyInjection.cs

@@ -7,8 +7,6 @@ public static class DependencyInjection
 {
     public static IServiceCollection AddInfrastructureServices(this IServiceCollection services, IConfiguration configuration)
     {
-        // Register infrastructure services here
-        // Example: services.AddSingleton<IMyService, MyService>();
         return services;
     }
 }