Added `<ImplicitUsings>` property with the value `enable` to both `DigitalData.MessagingService.Publisher.Abstraction.csproj` and `DigitalData.MessagingService.Client.DependencyInjection.csproj` to enable implicit global using directives. Adjusted the order of `<LangVersion>` to follow `<Nullable>` for consistency.
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.
