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/core/DigitalData.MessagingService.Application/Common/Interfaces/IEmailService.cs

@@ -14,5 +14,5 @@ public interface IEmailService
     /// Sends an email using the configured SMTP account.
     /// SMTP credentials are configured in appsettings.json (EmailAccount section).
     /// </summary>
-    Task SendEmailAsync(EmailAccountDto from, string to, string subject, string body, bool isHtml = true, CancellationToken cancellationToken = default);
+    Task SendEmailAsync(EmailAccountDto from, IEnumerable<string> recipients, string subject, string body, bool isHtml = true, CancellationToken cancellationToken = default);
 }

src/core/DigitalData.MessagingService.Application/EmailSending/Commands/SendEmailCommand.cs

@@ -15,9 +15,9 @@ public record SendEmailCommand : IRequest<OutgoingEmailEvent>
     public required GetSenderQuery Sender { get; init; }
 
     /// <summary>
-    /// Recipient email address
+    /// Recipient email addresses
     /// </summary>
-    public required string Recipient { get; init; }
+    public required IEnumerable<string> Recipients { get; init; }
 
     /// <summary>
     /// Email subject

src/core/DigitalData.MessagingService.Application/EmailSending/Validators/SendEmailCommandValidator.cs

@@ -10,13 +10,16 @@ public class SendEmailCommandValidator : AbstractValidator<SendEmailCommand>
 {
     public SendEmailCommandValidator()
     {
-        RuleFor(x => x.Recipient)
+        RuleFor(x => x.Recipients)
             .NotEmpty()
-            .WithMessage("Recipient is required")
-            .MaximumLength(200)
-            .WithMessage("Recipient must not exceed 200 characters")
-            .EmailAddress()
-            .WithMessage("Recipient must be a valid email address");
+            .WithMessage("Recipients are required")
+            .Must(x => x.Any())
+            .WithMessage("At least one recipient is required")
+            .ForEach(recipient => recipient
+                .NotEmpty()
+                .WithMessage("Recipient email must not be empty")
+                .EmailAddress()
+                .WithMessage("Invalid email address format"));
 
         RuleFor(x => x.Subject)
             .NotEmpty()

src/core/DigitalData.MessagingService.Publisher.Abstraction/OutgoingEmailEvent.cs

@@ -11,7 +11,7 @@ public record OutgoingEmailEvent
     /// <summary>
     /// Recipient email address
     /// </summary>
-    public string Recipient { get; set; } = null!;
+    public IEnumerable<string> Recipients { get; set; } = null!;
 
     /// <summary>
     /// Email subject