Fix transient nonexcl queues issue with RabbitMQ 4

[ono]

Summary

This updates the RabbitMQ 4 development/test setup and documentation for RabbitMQ’s deprecated transient_nonexcl_queues feature.

RabbitMQ 4 can deny non-durable, non-exclusive queues by default. Since Queue.declare(chan) uses AMQP’s historical defaults of durable: false and exclusive: false, users can hit a broker-initiated connection close when running against RabbitMQ 4.

Changes

• Add RabbitMQ 4 config to permit transient_nonexcl_queues for the local test container.
• Mount that config from docker-compose.rabbitmq4.yml.
• Remove the obsolete top-level Compose version field.
• Document why Queue.declare(chan) can trigger this RabbitMQ 4 error.
• Document alternatives:
  • use durable: true for durable named queues
  • use exclusive: true for private temporary queues
  • temporarily permit the deprecated feature in RabbitMQ config while migrating

Verification

• docker compose -f docker-compose.rabbitmq4.yml config
• docker compose -f docker-compose.rabbitmq4.yml up -d
• mix test

Result: 67 passed