RabbitMQ amqp091-go: Plaintext Credential Exposure via Exported PLAIN Authentication Struct Fields

RabbitMQ amqp091-go is a Go AMQP 0.9.1 client. Prior to 1.13.0, PlainAuth values defined in auth.go retain passwords as exported plaintext fields in Connection.Config.SASL after a successful PLAIN authentication handshake. The Connection.openComplete method in connection.go does not clear those values. Code with access to the Connection object, including reflective loggers, application performance monitoring agents, debugging utilities, and panic handlers, can traverse the configuration and expose the credentials to logs or state captures. The credential remains available for the lifetime of the connection instead of being cleared after authentication. This issue is fixed in version 1.13.0.