Support multiple email recipients in email-sending flow

Updated the `IEmailService` interface and related components to
support multiple recipients in the `SendEmailAsync` method.

- Replaced `Recipient` with `Recipients` in `SendEmailCommand`,
  `OutgoingEmailEvent`, and `EmailsController`.
- Updated `SendEmailCommandValidator` to validate a collection
  of recipients, ensuring at least one valid email address.
- Modified `LimilabsEmailService` to handle multiple recipients
  by iterating over the collection and adding each to the email.
- Adjusted `OutgoingEmailConsumer` to process and log multiple
  recipients.
- Updated logging and response structures to reflect the changes.

These changes enable the system to handle emails with multiple
recipients while maintaining proper validation and logging.

src/presentation/DigitalData.MessagingService.API/Controllers/EmailsController.cs

@@ -27,10 +27,7 @@ public class EmailsController(IMediator mediator) : ControllerBase
 
         return Accepted(new
         {
-            CommandId = outgoingEmailEvent.Id,
-            To = outgoingEmailEvent.Recipient,
-            outgoingEmailEvent.Subject,
-            outgoingEmailEvent.QueuedAt
+            outgoingEmailEvent.Id,
         });
     }
 }