Refactor solution structure and add RabbitMQ config

Reorganized the solution structure to align with a layered architecture:
- Replaced `src` folder with `core`, `infrastructure`, and `presentation`.
- Moved projects to their respective folders.
- Added `DigitalData.MessagingService.Publisher.Abstraction` project.
- Removed `DigitalData.MessagingService.Client` project.

Updated project configurations and nesting in the solution file.

Added `appsettings.Secrets.json` with RabbitMQ and email account settings:
- RabbitMQ configuration includes hostname, port, credentials, and queue/exchange details.
- Email configuration includes SMTP server details and credentials.

src/presentation/DigitalData.MessagingService.API/Program.cs

@@ -0,0 +1,87 @@
+using DigitalData.MessagingService.API.Middleware;
+using DigitalData.MessagingService.Application;
+using DigitalData.MessagingService.Application.Common.Dtos;
+using DigitalData.MessagingService.Infrastructure;
+using Serilog;
+
+// Configure Serilog early
+Log.Logger = new LoggerConfiguration()
+    .WriteTo.Console()
+    .WriteTo.File(
+        path: "logs/emailprofiler-.log",
+        rollingInterval: RollingInterval.Day,
+        retainedFileCountLimit: 30,
+        outputTemplate: "{Timestamp:yyyy-MM-dd HH:mm:ss.fff zzz} [{Level:u3}] {Message:lj}{NewLine}{Exception}")
+    .CreateBootstrapLogger();
+
+try
+{
+    Log.Information("Starting MessagingService API");
+
+    var builder = WebApplication.CreateBuilder(args);
+
+    // Use Serilog for logging
+    builder.Host.UseSerilog((context, services, configuration) => configuration
+        .ReadFrom.Configuration(context.Configuration)
+        .ReadFrom.Services(services)
+        .Enrich.FromLogContext()
+        .WriteTo.Console()
+        .WriteTo.File(
+            path: "logs/emailprofiler-.log",
+            rollingInterval: RollingInterval.Day,
+            retainedFileCountLimit: 30,
+            outputTemplate: "{Timestamp:yyyy-MM-dd HH:mm:ss.fff zzz} [{Level:u3}] {Message:lj}{NewLine}{Exception}"));
+
+    // Add appsettings.Secrets.json for sensitive configuration (not committed to git)
+    builder.Configuration.AddJsonFile("appsettings.Secrets.json", optional: true, reloadOnChange: true);
+
+    // Register Application layer (MediatR, AutoMapper, FluentValidation)
+    builder.Services.AddApplicationServices(builder.Configuration);
+
+    // Register Infrastructure layer (RabbitMQ, Repositories, etc.)
+    builder.Services.AddInfrastructure(builder.Configuration);
+
+    // Register EmailAccount configuration (IOptions<EmailAccountDto>)
+    builder.Services.Configure<EmailAccountDto>(
+        builder.Configuration.GetSection("EmailAccount"));
+
+    builder.Services.AddControllers();
+
+    builder.Services.AddEndpointsApiExplorer();
+    builder.Services.AddSwaggerGen();
+
+    var app = builder.Build();
+
+    // Add global exception handling middleware
+    app.UseMiddleware<ExceptionHandlingMiddleware>();
+
+    // Add Serilog request logging
+    app.UseSerilogRequestLogging();
+
+    // Configure the HTTP request pipeline.
+    if (app.Environment.IsDevelopment())
+    {
+        app.UseSwagger();
+        app.UseSwaggerUI();
+    }
+
+    app.UseHttpsRedirection();
+
+    app.UseAuthorization();
+
+    app.MapControllers();
+
+    Log.Information("MessagingService API started successfully");
+
+    app.Run();
+}
+catch (Exception ex)
+{
+    Log.Fatal(ex, "MessagingService API failed to start");
+    throw;
+}
+finally
+{
+    Log.CloseAndFlush();
+}
+