Refactor RabbitMQ email queue into publisher/consumer

Refactored the RabbitMQ-based email queue system by splitting
`OutgoingEmailQueue` into `OutgoingEmailPublisher` and
`OutgoingEmailConsumer` to separate publishing and consuming
responsibilities.

- Introduced `IOutgoingEmailConsumer` and renamed
  `IOutgoingEmailQueue` to `IOutgoingEmailPublisher` for clarity.
- Updated `SendEmailCommandHandler` to use the new publisher
  abstraction.
- Added `RabbitMqConnectionFactory` to centralize RabbitMQ
  connection management.
- Updated dependency injection to register new services.
- Simplified RabbitMQ initialization logic by delegating it to
  `RabbitMqConnectionFactory`.
- Enhanced logging for better observability.
- Improved modularity and maintainability by separating concerns
  between message publishing and consuming.

src/DigitalData.MessagingService.Application/Common/Interfaces/IOutgoingEmailConsumer.cs

@@ -0,0 +1,8 @@
+namespace DigitalData.MessagingService.Application.Common.Interfaces;
+
+/// <summary>
+/// Email queue interface for outgoing emails.
+/// </summary>
+public interface IOutgoingEmailConsumer
+{
+}

src/DigitalData.MessagingService.Application/Common/Interfaces/IOutgoingEmailPublisher.cs

@@ -6,7 +6,7 @@ namespace DigitalData.MessagingService.Application.Common.Interfaces;
 /// <summary>
 /// Email queue interface for outgoing emails.
 /// </summary>
-public interface IOutgoingEmailQueue
+public interface IOutgoingEmailPublisher
 {
     Task EnqueueAsync(OutgoingEmailEvent outgoingEmailEvent, CancellationToken cancellationToken = default);