Expose ConnectionFactory.MaxMessageSize on the transport configuration API

RabbitMQ client supports configuring the max message size since version [6.4.0](https://github.com/rabbitmq/rabbitmq-dotnet-client/blob/6.x/CHANGELOG.md#changes-between-631-and-640)

It might be helpful to expose the setting for users. Because in general is recommended for message payloads to be [reasonably small](https://particular.net/blog/putting-your-events-on-a-diet). 