Refactor email account handling for dynamic resolution

Reintroduced `EmailAccountDto` with conditional compilation to support both .NET and non-.NET environments. Updated `IEmailService` to accept `EmailAccountDto` as the sender, replacing reliance on pre-configured SMTP credentials.

Added `GetSenderQuery` and its handler to dynamically resolve email accounts based on `Id` or `Username`. Introduced `GetSenderQueryValidator` for validation, ensuring proper usage of the query.

Modified `SendEmailCommand` to include sender resolution via MediatR. Updated `OutgoingEmailEvent` to include sender information and adjusted `OutgoingEmailConsumer` and `LimilabsEmailService` to use the dynamically resolved sender.

Updated `EmailMappingProfile` to ignore the `Sender` property during mapping. Replaced `Name` with `Id` in `appsettings.Secrets.json` for email accounts. Removed the old `EmailAccountDto` folder and performed general cleanup and restructuring.

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

@@ -1,4 +1,7 @@
 using AutoMapper;
+using DigitalData.MessagingService.Application.Common.Dtos;
+using DigitalData.MessagingService.Application.EmailAccount.Queries;
+using DigitalData.MessagingService.Domain.Exceptions;
 using DigitalData.MessagingService.Publisher.Abstraction;
 using MediatR;
 
@@ -9,6 +12,8 @@ namespace DigitalData.MessagingService.Application.EmailSending.Commands;
 /// </summary>
 public record SendEmailCommand : IRequest<OutgoingEmailEvent>
 {
+    public required GetSenderQuery Sender { get; init; }
+
     /// <summary>
     /// Recipient email address
     /// </summary>
@@ -32,13 +37,20 @@ public record SendEmailCommand : IRequest<OutgoingEmailEvent>
 
 /// <summary>
 /// Handler for SendEmailCommand
-/// Creates EmailOutbox entity via AutoMapper and enqueues to RabbitMQ
+/// Resolves the sender account via MediatR, maps to OutgoingEmailEvent and enqueues to RabbitMQ
 /// </summary>
-public class SendEmailCommandHandler(IOutgoingEmailPublisher Publisher, IMapper Mapper) : IRequestHandler<SendEmailCommand, OutgoingEmailEvent>
+public class SendEmailCommandHandler(
+ISender Sender,
+IOutgoingEmailPublisher Publisher,
+IMapper Mapper) : IRequestHandler<SendEmailCommand, OutgoingEmailEvent>
 {
     public async Task<OutgoingEmailEvent> Handle(SendEmailCommand request, CancellationToken cancellationToken)
     {
-        var outgoingEmailEvent = Mapper.Map<OutgoingEmailEvent>(request);
+        var senderAccount = await Sender.Send(request.Sender, cancellationToken)
+            ?? throw new NotFoundException(
+                $"No email account found for the given sender criteria (Id: {request.Sender.Id}, Username: {request.Sender.Username}).");
+
+        var outgoingEmailEvent = Mapper.Map<OutgoingEmailEvent>(request) with { Sender = senderAccount };
 
         // Enqueue to RabbitMQ
         await Publisher.EnqueueAsync(outgoingEmailEvent, cancellationToken);