Refactor RabbitMQ DI into extension method

Refactored the registration of `RabbitMqConnectionFactory` and
RabbitMQ configuration into a new `AddRabbitMqConnectionFactory`
extension method for improved modularity and reusability.

- Removed direct calls to `AddSingleton<RabbitMqConnectionFactory>`
  and `Configure<RabbitMqConfiguration>` from the main
  `DependencyInjection` class.
- Added a new static `DependencyInjection` class under the
  `DigitalData.MessagingService.RabbitMQ` namespace.
- The new `AddRabbitMqConnectionFactory` method encapsulates
  RabbitMQ DI logic and accepts `IServiceCollection` and
  `IConfiguration` as parameters.
- Updated `DependencyInjection.cs` to use the new extension method.

src/DigitalData.MessagingService.Infrastructure/DependencyInjection.cs

@@ -34,11 +34,9 @@ public static class DependencyInjection
         // --- Email Queue (RabbitMQ) ---
         services.AddSingleton<OutgoingEmailConsumer>();
         services.AddSingleton<IOutgoingEmailPublisher, OutgoingEmailPublisher>();
-        services.AddSingleton<RabbitMqConnectionFactory>();
 
         // --- RabbitMQ Configuration ---
-        services.Configure<RabbitMqConfiguration>(
-            configuration.GetSection(RabbitMqConfiguration.SectionName));
+        services.AddRabbitMqConnectionFactory(configuration);
 
         // --- Data Protection (for encryption) ---
         services.AddDataProtection()

src/DigitalData.MessagingService.RabbitMQ/DependencyInjection.cs

@@ -0,0 +1,28 @@
+using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.DependencyInjection;
+
+namespace DigitalData.MessagingService.RabbitMQ
+{
+    /// <summary>
+    /// Dependency injection configuration for Infrastructure layer
+    /// </summary>
+    public static class DependencyInjection
+    {
+        /// <summary>
+        /// Adds Infrastructure layer services to the DI container
+        /// </summary>
+        public static IServiceCollection AddRabbitMqConnectionFactory(
+            this IServiceCollection services,
+            IConfiguration configuration)
+        {
+            services.AddSingleton<RabbitMqConnectionFactory>();
+
+            // --- RabbitMQ Configuration ---
+            services.Configure<RabbitMqConfiguration>(
+                configuration.GetSection(RabbitMqConfiguration.SectionName));
+
+            return services;
+        }
+    }
+
+}