MassTransit Transactional Messaging with .NET Aspire, RabbitMQ, Kafka, PostgreSQL, MongoDB, Outbox, Inbox, Retry, Error Queues, and Dead-Letter Handling

Build a .NET Aspire sample that uses MassTransit with RabbitMQ or Kafka, PostgreSQL transactional outbox and inbox state, retry, MassTransit error handling, broker-native dead-letter handling, and post-commit internal processing to update MongoDB after the write-side transaction commits.