Add support for email attachments in SendEmailCommand

Enhanced the email-sending workflow to support attachments:
- Updated `SendEmailCommand` with an `Attachments` property.
- Added `WithAttachments` method to handle attachment initialization.
- Modified `EmailsController` to accept file uploads via `IFormFileCollection`.
- Implemented `BuildAttachmentsAsync` to process uploaded files.
- Updated `EmailMappingProfile` to map `Attachments` to `EmailContext`.
- Adjusted `SendEmail` endpoint to consume `multipart/form-data`.
- Enhanced `SendEmail` response to include the queued event ID.
- Updated project file to include Swagger infrastructure folder.

These changes enable handling of email attachments and improve API functionality.

src/core/DigitalData.MessagingService.Application/Common/Mappings/EmailMappingProfile.cs

@@ -14,6 +14,7 @@ public class EmailMappingProfile : Profile
         // SendEmailCommand -> Email
         // Sender is resolved via MediatR in the handler and set separately after mapping.
         CreateMap<SendEmailCommand, EmailContext>()
-            .ForMember(dest => dest.Sender, opt => opt.Ignore());
+            .ForMember(dest => dest.Sender, opt => opt.Ignore())
+            .ForMember(dest => dest.Attachments, opt => opt.MapFrom(src => src.Attachments));
     }
 }