Introduced a new namespace `DigitalData.MessagingService.Publisher.Abstraction` in `OutgoingEmailCreateDto.cs` and `OutgoingEmailEvent.cs`.
Added a new record `OutgoingEmailCreateDto` with properties for recipient, subject, body, HTML flag, and queue timestamp.
Converted `OutgoingEmailEvent` from a class to a record.
Removed the unnecessary `using System;` directive from `OutgoingEmailEvent.cs`.
Reorganized the solution structure to align with a layered architecture:
- Replaced `src` folder with `core`, `infrastructure`, and `presentation`.
- Moved projects to their respective folders.
- Added `DigitalData.MessagingService.Publisher.Abstraction` project.
- Removed `DigitalData.MessagingService.Client` project.
Updated project configurations and nesting in the solution file.
Added `appsettings.Secrets.json` with RabbitMQ and email account settings:
- RabbitMQ configuration includes hostname, port, credentials, and queue/exchange details.
- Email configuration includes SMTP server details and credentials.
